XML 26 R22.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Mortgage Backed Securities Mortgage backed securities designated as AFS (Details) (USD $) In Thousands, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | $ 2,976,821us-gaap_InvestmentOwnedBalancePrincipalAmount |  |  | $ 2,621,540us-gaap_InvestmentOwnedBalancePrincipalAmount |
Available-for-sale MBS, Unamortized Premium (Discount) | 855,191dx_InvestmentsUnamortizedPremiumDiscount |  |  | 868,984dx_InvestmentsUnamortizedPremiumDiscount |
Available-for-sale MBS, Amortized Cost | 3,832,012us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis |  |  | 3,490,524us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis |
Available-for-sale Debt Securities, Gross Unrealized Gain | 61,411us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax |  |  | 48,868us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax |
Available-for-sale MBS, Gross Unrealized Loss | (13,700)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax |  |  | (23,153)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax |
Available-for-sale MBS, Fair Value | 3,879,723us-gaap_AvailableForSaleSecuritiesDebtSecurities |  |  | 3,516,239us-gaap_AvailableForSaleSecuritiesDebtSecurities |
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds | 102,923us-gaap_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceeds |  | 59,799us-gaap_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceeds |  |
Available-for-sale Securities, Gross Realized Gains | 1,773us-gaap_AvailableForSaleSecuritiesGrossRealizedGains |  | 219us-gaap_AvailableForSaleSecuritiesGrossRealizedGains |  |
Available-for-sale Securities, Gross Realized Losses | (465)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses |  | (3,526)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses |  |
Available-for-sale Securities, Gross Realized Gain (Loss) | 1,308us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet |  | (3,307)us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet |  |
Residential Mortgage Backed Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 2,018,979us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |  | 2,109,239us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Unamortized Premium (Discount) | 104,283dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |  | 113,618dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Amortized Cost | 2,123,262us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |  | 2,222,857us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 11,414us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |  | 8,580us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Gross Unrealized Loss | (13,154)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |  | (22,289)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Fair Value | 2,121,522us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  |  | 2,209,148us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Commercial Mortgage Backed Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 957,842us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |  | 512,301us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Unamortized Premium (Discount) | 8,870dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |  | 9,522dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Amortized Cost | 966,712us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |  | 521,823us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 27,834us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |  | 21,967us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Gross Unrealized Loss | (534)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |  | (555)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
Available-for-sale MBS, Fair Value | 994,012us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |  |  | 543,235us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
CMBS IO [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 0us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |  |  | 0us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |
Available-for-sale MBS, Unamortized Premium (Discount) | 742,038dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |  |  | 745,844dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |
Available-for-sale MBS, Amortized Cost | 742,038us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |  |  | 745,844us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 22,163us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |  |  | 18,321us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |
Available-for-sale MBS, Gross Unrealized Loss | (12)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |  |  | (309)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |
Available-for-sale MBS, Fair Value | 764,189us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |  |  | 763,856us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember |
Agency MBS [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 1,942,332us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 2,086,807us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Unamortized Premium (Discount) | 104,352dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 113,635dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Amortized Cost | 2,046,684us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 2,200,442us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 11,271us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 8,473us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Gross Unrealized Loss | (13,075)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | (22,215)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Fair Value | 2,044,880us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 2,186,700us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Weighted Average Coupon | 3.08%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [1] |  | 3.09%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [2]
Agency MBS [Member] | Commercial Mortgage Backed Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 740,363us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 301,943us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Unamortized Premium (Discount) | 17,321dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 18,042dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Amortized Cost | 757,684us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 319,985us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 20,234us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 15,288us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Gross Unrealized Loss | (171)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | (76)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Fair Value | 777,747us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 335,197us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Weighted Average Coupon | 3.68%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [1] |  | 5.21%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [2]
Agency MBS [Member] | CMBS IO [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 0us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [3] |  | 0us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [4]
Available-for-sale MBS, Unamortized Premium (Discount) | 410,948dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 426,564dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Amortized Cost |  |  |  | 426,564us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 13,257us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 12,252us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Gross Unrealized Loss | (12)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | (79)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Fair Value | 424,193us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 438,737us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Weighted Average Coupon | 0.87%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [1] |  | 0.80%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember | [2]
Notional balance for interest only securities | 10,415,002dx_Notionalbalanceforinterestonlysecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 10,460,113dx_Notionalbalanceforinterestonlysecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Non-Agency MBS [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 76,647us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 22,432us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Unamortized Premium (Discount) | (69)dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | (17)dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Amortized Cost | 76,578us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 22,415us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 143us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 107us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Gross Unrealized Loss | (79)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | (74)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Fair Value | 76,642us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 22,448us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Weighted Average Coupon | 3.57%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember | [1] |  | 3.83%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember | [2]
Non-Agency MBS [Member] | Commercial Mortgage Backed Securities [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 217,479us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  |  |
Available-for-sale MBS, Unamortized Premium (Discount) | (8,451)dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  |  |
Available-for-sale MBS, Amortized Cost | 209,028us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  |  |
Available-for-sale Debt Securities, Gross Unrealized Gain | 7,600us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  |  |
Available-for-sale MBS, Gross Unrealized Loss | (363)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  |  |
Available-for-sale MBS, Fair Value | 216,265us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 208,038us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Weighted Average Coupon | 4.23%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember | [1] |  | 5.10%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember | [2]
Non-Agency MBS [Member] | CMBS IO [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Par Balance | 0us-gaap_InvestmentOwnedBalancePrincipalAmount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember | [3] |  |  |
Available-for-sale MBS, Unamortized Premium (Discount) | 331,090dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 319,280dx_InvestmentsUnamortizedPremiumDiscount / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Amortized Cost | 331,090us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 319,280us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale Debt Securities, Gross Unrealized Gain | 8,906us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 6,069us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Gross Unrealized Loss | 0us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | (230)us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Fair Value | 339,996us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 325,119us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Weighted Average Coupon | 0.71%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember | [1] |  | 0.72%dx_InvestmentsWeightedAverageCouponRate / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember | [2]
Notional balance for interest only securities | 9,115,887dx_Notionalbalanceforinterestonlysecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 7,868,896dx_Notionalbalanceforinterestonlysecurities / us-gaap_DebtSecurityAxis = us-gaap_InterestOnlyStripMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Agency MBS [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 261,035us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 322,741us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 531us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 879us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Less than One Year | 17us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 24us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,030,027us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 1,321,323us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 12,727us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 21,491us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Greater than or Equal to One Year | 91us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |  |  | 113us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
Non-Agency MBS [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Available-for-sale MBS, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 79,310us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 111,778us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 382us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 625us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Less than One Year | 13us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 24us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,224us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 18,037us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 61us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | $ 159us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
Available-for-sale MBS, Number of Securities in Continuous Unrealized Loss Position for Greater than or Equal to One Year | 4us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |  |  | 5us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_FairValueByAssetClassAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember |
[1] | (1) The current weighted average coupon ("WAC") is the gross interest rate of the pool of mortgages underlying the security weighted by the outstanding principal balance (or by notional balance in the case of an IO security).
[2] | (1)The current weighted average coupon ("WAC") is the gross interest rate of the pool of mortgages underlying the security weighted by the outstanding principal balance (or by notional balance in the case of an IO security).
[3] | (2)The notional balance for Agency CMBS IO and non-Agency CMBS IO was $10,415,002 and $9,115,887, respectively, as of March 31, 2015.
[4] | (2) The notional balance for the Agency CMBS IO and non-Agency CMBS IO was $10,460,113 and $7,868,896, respectively, as of December 31, 2014.

X
- Definition The remaining amount of investment premium (discount), net, originally recognized at the purchase date of the instruments that has yet to be amortized (accreted) into earnings. + References No definition available. + Details
Name: | dx_InvestmentsUnamortizedPremiumDiscount
Namespace Prefix: | dx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the current weighted-average gross interest rate earned on this type of MBS in the investment portfolio as of the period indicated. The gross interest rate of each MBS within the portfolio is weighted based on its current outstanding notional or par balance. The current outstanding notional or par balance for each MBS consists of the total of all principal balances remaining on the mortgage loans underlying each MBS. + References No definition available. + Details
Name: | dx_InvestmentsWeightedAverageCouponRate
Namespace Prefix: | dx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Notional balance for interest only securities owned by the Company. Interest only securities represent the right to receive excess interest payments, and not principal cash flows, based on the underlying unpaid principal balance (ie, notional) of the underlying pool of mortgage loans. + References No definition available. + Details
Name: | dx_Notionalbalanceforinterestonlysecurities
Namespace Prefix: | dx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of debt securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -Subparagraph (b)-(g) -URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceeds
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of investment positions in available-for-sale investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
Name: | us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of investment positions in available-for-sale investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition For investments which are quantified by principal amount, the principle balance held at close of period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-12C.Column B) -URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611225-123010 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14.Column B) -URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611322-123010 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-12.Column B) -URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611133-123010 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12C -Paragraph Column B -Article 12 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Paragraph Column B -Article 12 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 14 -Paragraph Column B -Article 12 + Details
Name: | us-gaap_InvestmentOwnedBalancePrincipalAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DebtSecurityAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtSecurityAxis=us-gaap_InterestOnlyStripMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtSecurityAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |