Loans (Activity in Allowance for Loan Losses by Portfolio Segment) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 135,859	$ 99,542	$ 92,438
Provision for loan losses	51,673	51,845	16,314
Charge-offs	(48,328)	(29,572)	(28,485)
Recoveries	13,841	14,044	19,275
Net charge-offs	(34,487)	(15,528)	(9,210)
Ending balance	153,045	135,859	99,542
Individually evaluated for impairment	9,186	4,378	1,680
Collectively evaluated for impairment	143,859	131,481	97,862
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	42,993	44,273	46,700
Provision for loan losses	22,181	5,255	484
Charge-offs	(15,910)	(11,092)	(12,073)
Recoveries	3,651	4,557	9,162
Net charge-offs	(12,259)	(6,535)	(2,911)
Ending balance	52,915	42,993	44,273
Individually evaluated for impairment	5,436	2,378	1,613
Collectively evaluated for impairment	47,479	40,615	42,660
Commercial And Industrial Energy Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	54,696	14,919	6,090
Provision for loan losses	24,545	45,774	10,066
Charge-offs	(18,644)	(6,000)	(1,747)
Recoveries	56	3	510
Net charge-offs	(18,588)	(5,997)	(1,237)
Ending balance	60,653	54,696	14,919
Individually evaluated for impairment	3,750	2,000	67
Collectively evaluated for impairment	56,903	52,696	14,852
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	24,313	27,163	22,590
Provision for loan losses	5,064	(3,182)	6,573
Charge-offs	(82)	(657)	(3,800)
Recoveries	918	989	1,800
Net charge-offs	836	332	(2,000)
Ending balance	30,213	24,313	27,163
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	30,213	24,313	27,163
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	4,659	5,178	5,230
Provision for loan losses	(164)	(428)	681
Charge-offs	(814)	(577)	(1,097)
Recoveries	557	486	364
Net charge-offs	(257)	(91)	(733)
Ending balance	4,238	4,659	5,178
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	4,238	4,659	5,178
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,198	8,009	5,010
Provision for loan losses	47	4,426	5,328
Charge-offs	(12,878)	(11,246)	(9,768)
Recoveries	8,659	8,009	7,439
Net charge-offs	(4,219)	(3,237)	(2,329)
Ending balance	5,026	9,198	8,009
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	5,026	9,198	8,009
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	0	0	6,818
Provision for loan losses	0	0	(6,818)
Charge-offs	0	0	0
Recoveries	0	0	0
Net charge-offs	0	0	0
Ending balance	0	0	0
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	$ 0	$ 0	$ 0