Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs (Detail) - TDR Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Troubled Debt Restructuring Activity [Roll Forward]
Beginning Balance	$ 23,608	$ 27,853
Additions	445	24,619	$ 20,436
Ending Balance	5,067	23,608	27,853
Accruing
Troubled Debt Restructuring Activity [Roll Forward]
Beginning Balance	3,704	23,770	6,867
Additions	120	804	4,847
Net payments	(774)	(1,440)	(723)
Returned to performing status	0	(20,656)	(5,529)
Net transfers (to) from non-accrual	(307)	1,226	18,308
Ending Balance	2,743	3,704	23,770
Non-Accrual
Troubled Debt Restructuring Activity [Roll Forward]
Beginning Balance	19,904	4,083	10,924
Additions	325	23,815	15,589
Net payments	(15,525)	1,991	(1,359)
Charge-offs	(2,687)	(8,457)	(1,880)
Transfers to OREO	0	(302)	(77)
Loans sold	0	0	(806)
Net transfers from (to) accruing	307	(1,226)	(18,308)
Ending Balance	$ 2,324	$ 19,904	$ 4,083