Fair Value Measurements - Additional Information (Details) - USD ($)	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Borrowings	$ 421,000,000	$ 1,250,000,000
Impaired loans measured at nonrecurring basis	When the fair value of the collateral is based on an observable market price or a current appraised value, we measure the impaired loan at Level 2. When an appraised value is not available, or management determines the fair value of the collateral is further impaired below the appraised value and there is no observable market price or a discounted cash flow has been used to determine the fair value, we measure the impaired loan at Level 3.
Real estate owned (“REO”)	$ 1,400,000	1,734,000
Fair Value Measurement Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepayment rate	15.00%
Borrowings	$ 15,000,000	0
Line of credit, borrowing capacity	25,000,000
Total collateral dependent impaired loans	14,400,000	9,000,000
Reserves related to impaired loans	0	0
Real estate owned (“REO”)	$ 1,400,000	$ 1,700,000
Fair Value Measurement Level 3 \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate	4.00%
Fair Value Measurement Level 3 \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate	10.00%

Impaired collateral dependent loans fair value disclosure.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

+ References

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- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Describes the policies and procedures for identifying and measuring losses on loans when the present value of expected cash flows discounted at the loan's effective interest rate, or, alternatively, a loan's observable market price or fair value of the underlying collateral is less than the carrying amount of the loan, and sets forth the amount of the loss. Also sets forth material facts pertaining to significant loan modifications in a troubled debt restructuring, describes the method for valuing a loan deemed to be impaired or nonperforming, indicates whether income on impaired or nonperforming loans are being recognized and describes the method for recognizing the income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 35
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=84230098&loc=d3e2555-111518

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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Amount of real estate investments, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; (7) other real estate investments; (8) real estate joint ventures; and (9) unconsolidated real estate and other joint ventures not separately presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(d))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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