Borrowings Under Repurchase Agreements - Weighted Average Maturities and Interest Rates of Borrowings (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt Balance	$ 1,091,316
JP Morgan Chase [Member]
Debt Instrument [Line Items]
Long-term debt	115,375
Line of Credit [Member]
Debt Instrument [Line Items]
Debt Balance	$ 1,091,316	$ 925,774
Weighted Average Remaining Maturity	2 years 5 months 24 days	2 years 8 months 12 days
Weighted Average Rate	2.90%	2.90%
Long-term debt	$ 1,091,316
Line of Credit [Member] \| UBS [Member]
Debt Instrument [Line Items]
Debt Balance	$ 133,899	$ 133,899
Weighted Average Remaining Maturity	2 years 6 months	2 years 8 months 12 days
Weighted Average Rate	2.80%	2.80%
Long-term debt	$ 133,899
Line of Credit [Member] \| DB Facility [Member]
Debt Instrument [Line Items]
Debt Balance	$ 276,868	$ 300,005
Weighted Average Remaining Maturity	2 years	2 years 3 months 18 days
Weighted Average Rate	3.70%	3.70%
Long-term debt	$ 276,868
Line of Credit [Member] \| JP Morgan Chase [Member]
Debt Instrument [Line Items]
Debt Balance	$ 635,676	$ 445,942
Weighted Average Remaining Maturity	2 years 9 months 24 days	3 years 1 month 6 days
Weighted Average Rate	2.60%	2.60%
Long-term debt	$ 635,676
Line of Credit [Member] \| Goldman Sachs [Member]
Debt Instrument [Line Items]
Debt Balance	$ 44,873	$ 45,928
Weighted Average Remaining Maturity	3 years 1 month 6 days	3 years 3 months 18 days
Weighted Average Rate	4.00%	3.80%
Long-term debt	$ 44,873
Line of Credit [Member] \| Goldman Sachs [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis point	3.50%	3.50%
Minimum [Member] \| Line of Credit [Member] \| DB Facility [Member] \| Three Month LIBOR [Member]
Debt Instrument [Line Items]
Basis point	1.80%	1.80%
Minimum [Member] \| Line of Credit [Member] \| JP Morgan Chase [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis point	2.25%	2.25%
Maximum [Member] \| Line of Credit [Member] \| DB Facility [Member] \| Three Month LIBOR [Member]
Debt Instrument [Line Items]
Basis point	2.32%	2.32%
Maximum [Member] \| Line of Credit [Member] \| JP Morgan Chase [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis point	3.50%	3.50%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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- Definition

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

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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- Definition

Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20, 22
-Article 5

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 7

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- Definition

Weighted average interest rate of long-term debt outstanding.

+ References

No definition available.

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