Balance Sheet Offsetting - Schedule of Balance Sheet Offsetting (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Offsetting Assets Liabilities [Line Items]
Financial liabilities, Gross Amounts Recognized in the Condensed Consolidated Balance Sheets	$ 605,626	$ 700,052
Financial liabilities, Gross Amounts offset in the Condensed Consolidated Balance Sheets	0	(4)
Financial liabilities, Net Amounts of Assets presented in the Condensed Consolidated Balance Sheets	605,626	700,048
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	0	4
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Pledged	(645,980)	(737,674)
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Net Amount	(40,354)	(37,622)
Repurchase Agreements [Member]
Offsetting Assets Liabilities [Line Items]
Financial liabilities, Gross Amounts Recognized in the Condensed Consolidated Balance Sheets	590,465	690,704
Financial liabilities, Gross Amounts offset in the Condensed Consolidated Balance Sheets	0	0
Financial liabilities, Net Amounts of Assets presented in the Condensed Consolidated Balance Sheets	590,465	690,704
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	0	0
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Pledged	(629,189)	(721,102)
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Net Amount	(38,724)	(30,398)
Interest Rate Swaps [Member]
Offsetting Assets Liabilities [Line Items]
Financial assets, Gross Amounts Recognized in the Condensed Consolidated Balance Sheets	15,161	9,344
Financial assets, Gross Amounts offset in the Condensed Consolidated Balance Sheets	0	0
Financial assets, Net Amounts of Assets presented in the Condensed Consolidated Balance Sheets	0	0
Financial assets, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	15,161	9,344
Financial assets, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Pledged	0	0
Financial assets, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Net Amount	15,161	9,344
Interest Rate Swaps [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Offsetting Assets Liabilities [Line Items]
Financial assets, Gross Amounts Recognized in the Condensed Consolidated Balance Sheets	15,161	9,344
Financial assets, Gross Amounts offset in the Condensed Consolidated Balance Sheets	0	0
Financial assets, Net Amounts of Assets presented in the Condensed Consolidated Balance Sheets	0	0
Financial assets, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	15,161	9,344
Financial assets, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Pledged	0	0
Financial assets, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Net Amount	15,161	9,344
Financial liabilities, Gross Amounts Recognized in the Condensed Consolidated Balance Sheets	15,161	9,348
Financial liabilities, Gross Amounts offset in the Condensed Consolidated Balance Sheets	0	(4)
Financial liabilities, Net Amounts of Assets presented in the Condensed Consolidated Balance Sheets	15,161	9,344
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Financial Instruments	0	4
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Collateral Pledged	(16,791)	(16,572)
Financial liabilities, Gross Amounts Not Offset in the Condensed Consolidated Balance Sheets, Net Amount	$ (1,630)	$ (7,224)