Balance Sheet Offsetting (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Offsetting Liabilities
Gross Amounts Recognized	$ 179,896	$ 224,212
Gross Amounts Offset	0	0
Net Amounts Presented	179,896	224,212
Gross Amounts Not Offset, Financial Instruments	(725)	(5,376)
Gross Amounts Not Offset, Cash Collateral	(151,874)	(208,141)
Net Amount	27,297	10,695
Collateral posted with derivatives counterparties	41,300	51,400
Repurchase agreements
Offsetting Repurchase Agreement Liabilities
Gross Amounts Recognized	150,000	200,000
Gross Amounts Offset	0	0
Net Amounts Presented	150,000	200,000
Gross Amounts Not Offset, Financial Instruments	0	0
Gross Amounts Not Offset, Cash Collateral	(150,000)	(200,000)
Net Amount	0	0
Interest rate caps and swaps
Offsetting Assets
Gross Amounts Recognized	25,776	26,346
Gross Amounts Offset	0	0
Net Amounts Presented	25,776	26,346
Gross Amounts Not Offset, Financial Instruments	(725)	(5,376)
Gross Amounts Not Offset, Cash Collateral	0	0
Net Amount	25,051	20,970
Offsetting Liabilities
Gross Amounts Recognized	29,896	24,212
Gross Amounts Offset	0	0
Net Amounts Presented	29,896	24,212
Gross Amounts Not Offset, Financial Instruments	(725)	(5,376)
Gross Amounts Not Offset, Cash Collateral	(1,874)	(8,141)
Net Amount	$ 27,297	$ 10,695