Loans, Leases and Allowance for Credit Losses - Allowances for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Valuation Allowance [Line Items]
Beginning Balance				$ 110,216				$ 100,050	$ 110,216	$ 100,050	$ 95,427
Charge-offs									6,497	7,662	21,479
Recoveries									(12,149)	(13,102)	(12,882)
Provision for credit losses	$ 2,500	$ 0	$ 0	700	$ 300	$ 419	$ 507	3,500	3,200	4,726	13,220
Ending balance	119,068				110,216				119,068	110,216	100,050
Construction and land development [Member]
Valuation Allowance [Line Items]
Beginning Balance				18,558				14,519	18,558	14,519	10,554
Charge-offs									0	87	1,538
Recoveries									(1,872)	(2,160)	(2,060)
Provision for credit losses									(1,454)	1,966	3,443
Ending balance	18,976				18,558				18,976	18,558	14,519
Commercial real estate [Member]
Valuation Allowance [Line Items]
Beginning Balance				28,783				32,064	28,783	32,064	34,982
Charge-offs									0	964	8,648
Recoveries									(4,139)	(3,859)	(2,758)
Provision for credit losses									(9,762)	(6,176)	2,972
Ending balance	23,160				28,783				23,160	28,783	32,064
Residential real estate [Member]
Valuation Allowance [Line Items]
Beginning Balance				7,456				11,640	7,456	11,640	15,237
Charge-offs									820	1,728	5,922
Recoveries									(2,181)	(1,896)	(2,097)
Provision for credit losses									(3,539)	(4,352)	228
Ending balance	5,278				7,456				5,278	7,456	11,640
Commercial and industrial [Member]
Valuation Allowance [Line Items]
Beginning Balance				54,566				39,657	54,566	39,657	32,860
Charge-offs									5,550	4,370	4,000
Recoveries									(3,754)	(4,728)	(5,037)
Provision for credit losses									18,411	14,551	5,760
Ending balance	71,181				54,566				71,181	54,566	39,657
Consumer [Member]
Valuation Allowance [Line Items]
Beginning Balance				$ 853				$ 2,170	853	2,170	1,794
Charge-offs									127	513	1,371
Recoveries									(203)	(459)	(930)
Provision for credit losses									(456)	(1,263)	817
Ending balance	$ 473				$ 853				$ 473	$ 853	$ 2,170