Loans, Leases and Allowance for Credit Losses - Allowances for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation Allowance [Line Items]
Beginning Balance				$ 100,050				$ 95,427	$ 100,050	$ 95,427	$ 99,170
Charge-offs									(7,662)	(21,479)	(61,286)
Recoveries									13,102	12,882	10,699
Provision for credit losses	300	419	507	3,500	4,300	0	3,481	5,439	4,726	13,220	46,844
Ending balance	110,216				100,050				110,216	100,050	95,427
Construction and land development [Member]
Valuation Allowance [Line Items]
Beginning Balance				14,519				10,554	14,519	10,554	14,195
Charge-offs									(87)	(1,538)	(10,992)
Recoveries									2,160	2,060	2,903
Provision for credit losses									1,966	3,443	4,448
Ending balance	18,558				14,519				18,558	14,519	10,554
Commercial real estate [Member]
Valuation Allowance [Line Items]
Beginning Balance				32,064				34,982	32,064	34,982	35,031
Charge-offs									(964)	(8,648)	(19,166)
Recoveries									3,859	2,758	3,294
Provision for credit losses									(6,176)	2,972	15,823
Ending balance	28,783				32,064				28,783	32,064	34,982
Residential real estate [Member]
Valuation Allowance [Line Items]
Beginning Balance				11,640				15,237	11,640	15,237	19,134
Charge-offs									(1,728)	(5,922)	(7,063)
Recoveries									1,896	2,097	1,078
Provision for credit losses									(4,352)	228	2,088
Ending balance	7,456				11,640				7,456	11,640	15,237
Commercial and industrial [Member]
Valuation Allowance [Line Items]
Beginning Balance				39,657				32,860	39,657	32,860	25,535
Charge-offs									(4,370)	(4,000)	(17,341)
Recoveries									4,728	5,037	3,067
Provision for credit losses									14,551	5,760	21,599
Ending balance	54,566				39,657				54,566	39,657	32,860
Consumer [Member]
Valuation Allowance [Line Items]
Beginning Balance				2,170				1,794	2,170	1,794	5,275
Charge-offs									(513)	(1,371)	(6,724)
Recoveries									459	930	357
Provision for credit losses									(1,263)	817	2,886
Ending balance	$ 853				$ 2,170				$ 853	$ 2,170	$ 1,794