Allowance for Credit Losses - Interest Income Recognized on Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 768,501	$ 852,027	$ 1,001,641
Interest income recognized, Total	27,643	27,799	35,560
Interest income recognized, Cash basis	19,046	18,573	25,451
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	166,628	184,773	197,533
Interest income recognized, Total	6,243	4,029	4,852
Interest income recognized, Cash basis	6,243	4,029	4,852
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	236,201	181,932	155,188
Interest income recognized, Total	2,933	2,251	7,197
Interest income recognized, Cash basis	2,933	2,251	7,197
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	59,457	91,149	147,288
Interest income recognized, Total	335	142	1,043
Interest income recognized, Cash basis	335	142	796
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	20,276	62,734	96,475
Interest income recognized, Total	2,311	1,893	5,248
Interest income recognized, Cash basis	2,311	1,893	5,248
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	101,483	126,005	183,059
Interest income recognized, Total	6,188	9,180	6,203
Interest income recognized, Cash basis	4,037	6,978	4,111
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	118,449	133,800	149,461
Interest income recognized, Total	6,380	6,613	6,784
Interest income recognized, Cash basis	2,638	2,546	2,341
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	21,523	18,083	12,811
Interest income recognized, Total	905	750	683
Interest income recognized, Cash basis	261	248	183
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	25,675	35,173	44,116
Interest income recognized, Total	1,619	2,251	2,916
Interest income recognized, Cash basis	175	295	515
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	18,809	18,378	15,710
Interest income recognized, Total	729	690	634
Interest income recognized, Cash basis	$ 113	$ 191	$ 208