Loans, Leases and Allowance for Credit Losses - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Leases [Line Items]
Receivable with Imputed Interest, Discount		$ (8,200)	$ (7,500)
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	48,381	67,659
Impaired Financing Receivable, Average Recorded Investment		150,151	169,758	$ 182,670
Aggregate carrying amount of impaired loans	[2]	24,287	124,928
Reduction in interest income due to nonaccrual loans		2,500	3,800	5,400
Loans And Loans Receivable Purchases		137,200	166,400
Financing Receivable, Significant Sales		102,200
Impaired loans with no allowance recorded	[3]	104,587	41,822
Impaired loans with an allowance recorded	[4]	4,658	10,765
Loans and Leases Receivable, Gain (Loss) on Sales, Net		500
Troubled Debt Restructured Loans [Member]
Leases [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status		18,200	53,600
Impaired Financing Receivable, Average Recorded Investment		113,900	126,600	$ 141,800
Aggregate carrying amount of impaired loans		3,000	103,300
Loan commitments outstanding		100	1,200
Impaired loans with no allowance recorded		85,900	35,000
Impaired loans with an allowance recorded		300	8,900
Construction and land development [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		0	21,052
Loans And Loans Receivable Purchases		100
Impaired loans with no allowance recorded		18,322	696
Impaired loans with an allowance recorded		0	3,112
Commercial real estate [Member]
Leases [Line Items]
Loans And Loans Receivable Purchases		13,200
Residential real estate [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		914	19,300
Impaired loans with no allowance recorded		15,661	0
Impaired loans with an allowance recorded		270	1,052
Commercial and industrial [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		18,230	11,399
Loans And Loans Receivable Purchases		117,100
Impaired loans with no allowance recorded		8,283	2,350
Impaired loans with an allowance recorded		3,518	1,926
Consumer [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		21	175
Impaired loans with no allowance recorded		313	188
Impaired loans with an allowance recorded		1	$ 17
Leases [Member]
Leases [Line Items]
Loans And Loans Receivable Purchases		$ 6,800

[1] Includes non-accrual TDR loans of $18.2 million and $53.6 million at December 31, 2015 and 2014, respectively.

[2] Includes TDR loans of $3.0 million and $103.3 million at December 31, 2015 and 2014, respectively.

[3] Includes TDR loans of $85.9 million and $35.0 million at December 31, 2015 and 2014, respectively.

[4] Includes valuation allowance related to TDR loans of $0.3 million and $8.9 million at December 31, 2015 and 2014, respectively.