Derivative Financial Instruments (Offsetting Derivatives) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative instrument assets, Gross Amount	$ 6,517	$ 35,727
Derivative instrument asset, Amount Offset	(30,700)
Derivative Asset	1,035	0
Liability Derivatives, Fair Value, Gross Liability	4,987	25,300
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(2,600)
Derivative liability	186	446
Hedge Accounting Positions [Member]
Derivative [Line Items]
Derivative instrument assets, Gross Amount	2,198	3,270
Derivative instrument asset, Amount Offset, Total	(1,046)	(2,335)
Derivative instrument asset, Amount Offset	(398)	(935)
Derivative Asset	754	0
Liability Derivatives, Fair Value, Gross Liability	367	792
Derivative instrument liability, Amount Offset, Total	(367)	(792)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0	0
Derivative liability	0	0
Non-Hedged Accounting Positions [Member]
Derivative [Line Items]
Derivative instrument assets, Gross Amount	4,319	32,457
Derivative instrument asset, Amount Offset, Total	(2,756)	(21,917)
Derivative instrument asset, Amount Offset	(1,282)	(10,540)
Derivative Asset	281	0
Liability Derivatives, Fair Value, Gross Liability	4,620	24,508
Derivative instrument liability, Amount Offset, Total	(3,435)	(23,462)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(999)	(600)
Derivative liability	186	446
Subject to and not subject to Master Netting Agreements [Member]
Derivative [Line Items]
Derivative instrument asset, Amount Offset, Total	(3,802)	(24,252)
Derivative instrument asset, Amount Offset	(1,680)	(11,475)
Derivative Asset	43,177	41,910
Derivative instrument liability, Amount Offset, Total	(3,802)	(24,254)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(999)	(600)
Derivative liability	$ 16,644	$ 20,335