Balance Sheet Offsetting (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Offsetting Liabilities
Gross Amounts Recognized	$ 223,737	$ 206,911
Gross Amounts Offset	0	0
Net Amounts Presented	223,737	206,911
Gross Amounts Not Offset, Financial Instruments	(3,888)	(5,268)
Gross Amounts Not Offset, Cash Collateral	(209,314)	(201,643)
Net Amount	10,535	0
Collateral posted with counterparties	59,600	52,400
Repurchase Agreements
Offsetting Repurchase Agreement Liabilities
Gross Amounts Recognized	200,000	165,000
Gross Amounts Offset	0	0
Net Amounts Presented	200,000	165,000
Gross Amounts Not Offset, Financial Instruments	0	0
Gross Amounts Not Offset, Cash Collateral	(200,000)	(165,000)
Net Amount	0	0
Interest Rate Caps and Swaps
Offsetting Assets
Gross Amounts Recognized	26,586	26,087
Gross Amounts Offset	0	0
Net Amounts Presented	26,586	26,087
Gross Amounts Not Offset, Financial Instruments	(3,888)	(5,268)
Gross Amounts Not Offset, Cash Collateral	0	0
Net Amount	22,698	20,819
Offsetting Derivative Liabilities
Gross Amounts Recognized	23,737	41,911
Gross Amounts Offset	0	0
Net Amounts Presented	23,737	41,911
Gross Amounts Not Offset, Financial Instruments	(3,888)	(5,268)
Gross Amounts Not Offset, Cash Collateral	(9,314)	(36,643)
Net Amount	$ 10,535	$ 0