Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 769,259	$ 768,501	$ 852,027
Interest income recognized, Total	31,397	27,643	27,799
Interest income recognized, Cash basis	21,885	19,046	18,573
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	175,877	166,628	184,773
Interest income recognized, Total	4,878	6,243	4,029
Interest income recognized, Cash basis	4,878	6,243	4,029
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	277,647	236,201	181,932
Interest income recognized, Total	8,342	2,933	2,251
Interest income recognized, Cash basis	8,342	2,933	2,251
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	29,237	59,457	91,149
Interest income recognized, Total	2,300	335	142
Interest income recognized, Cash basis	2,300	335	142
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	19,697	20,276	62,734
Interest income recognized, Total	644	2,311	1,893
Interest income recognized, Cash basis	644	2,311	1,893
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	98,394	101,483	126,005
Interest income recognized, Total	6,227	6,188	9,180
Interest income recognized, Cash basis	3,154	4,037	6,978
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	103,060	118,449	133,800
Interest income recognized, Total	5,999	6,380	6,613
Interest income recognized, Cash basis	1,975	2,638	2,546
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	36,493	21,523	18,083
Interest income recognized, Total	1,325	905	750
Interest income recognized, Cash basis	410	261	248
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	19,636	25,675	35,173
Interest income recognized, Total	1,242	1,619	2,251
Interest income recognized, Cash basis	99	175	295
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	9,218	18,809	18,378
Interest income recognized, Total	440	729	690
Interest income recognized, Cash basis	$ 83	$ 113	$ 191