Derivative Instruments and Other Hedging Activities - Reconciliation of Gross Amounts in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Derivative assets
Gross Amounts Presented in the Balance Sheet	$ 50,713	$ 24,393
Gross amounts not offset in the Balance Sheet, derivatives	(3,784)	0
Gross amounts not offset in the Balance Sheet, collateral	0	(45)
Net	46,929	24,348
Derivative liabilities
Gross Amounts Presented in the Balance Sheet	53,441	18,058
Gross amounts not offset in the Balance Sheet, derivatives	(3,784)	0
Gross amounts not offset in the Balance Sheet, collateral	(14,197)	(9,428)
Net	35,460	8,630
Written and Purchased Options
Derivative assets
Gross Amounts Presented in the Balance Sheet	7,144	6,277
Gross amounts not offset in the Balance Sheet, derivatives	(3,784)	0
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net	3,360	6,277
Designated as Hedging Instrument | Interest Rate Contracts
Derivative assets
Gross Amounts Presented in the Balance Sheet		58
Gross amounts not offset in the Balance Sheet, derivatives		0
Gross amounts not offset in the Balance Sheet, collateral		(45)
Net		13
Derivative liabilities
Gross Amounts Presented in the Balance Sheet	9,872
Gross amounts not offset in the Balance Sheet, derivatives	(3,784)
Gross amounts not offset in the Balance Sheet, collateral	(3,072)
Net	3,016
Not Designated as Hedging Instruments | Interest Rate Contracts
Derivative assets
Gross Amounts Presented in the Balance Sheet	43,569	18,058
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net	43,569	18,058
Derivative liabilities
Gross Amounts Presented in the Balance Sheet	43,569	18,058
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	(11,125)	(9,428)
Net	$ 32,444	$ 8,630