Loans and Allowance for Loan Losses (Allowance for Loan Losses by Portfolio Class) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 229,418	$ 181,179
Allowance for loan losses: Net provision for loan losses	58,968	110,659	$ 73,038
Allowance for loan losses: (Decrease) increase in FDIC loss share receivable	(2,526)	(3,957)
Allowance for loan losses: Ending balance	217,308	229,418	181,179
Allowance for loan losses: Individually evaluated for impairment	18,566	29,295
Allowance for loan losses: Amounts related to purchased credit impaired loans	14,107	18,353
Allowance for loan losses: Collectively evaluated for impairment	184,635	181,770
Loans: Individually evaluated for impairment	317,197	301,345
Loans: Purchased credit impaired loans	147,537	190,915
Loans: Collectively evaluated for impairment	18,539,429	16,259,891
Loans receivable	19,004,163	16,752,151
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	13,509	6,041
Allowance for loan losses: Ending balance	13,709	13,509	6,041
Allowance for loan losses: Individually evaluated for impairment	1,326	466
Allowance for loan losses: Amounts related to purchased credit impaired loans	41	253
Allowance for loan losses: Collectively evaluated for impairment	12,342	12,790
Loans: Individually evaluated for impairment	15,530	15,376
Loans: Purchased credit impaired loans	2,742	7,928
Loans: Collectively evaluated for impairment	2,366,327	1,990,586
Loans receivable	2,384,599	2,013,890
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	6,271	5,642
Allowance for loan losses: Ending balance	7,372	6,271	5,642
Allowance for loan losses: Individually evaluated for impairment	11	38
Allowance for loan losses: Amounts related to purchased credit impaired loans	172	406
Allowance for loan losses: Collectively evaluated for impairment	7,189	5,827
Loans: Individually evaluated for impairment	363	1,938
Loans: Purchased credit impaired loans	5,829	5,271
Loans: Collectively evaluated for impairment	1,367,229	1,003,670
Loans receivable	1,373,421	1,010,879
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	25,361	25,353
Allowance for loan losses: Ending balance	24,844	25,361	25,353
Allowance for loan losses: Individually evaluated for impairment	189	91
Allowance for loan losses: Amounts related to purchased credit impaired loans	12,258	15,043
Allowance for loan losses: Collectively evaluated for impairment	12,397	10,227
Loans: Individually evaluated for impairment	10,640	4,347
Loans: Purchased credit impaired loans	119,553	141,992
Loans: Collectively evaluated for impairment	2,560,279	2,000,374
Loans receivable	2,690,472	2,146,713
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	26,142	24,857
Allowance for loan losses: Ending balance	30,503	26,142	24,857
Allowance for loan losses: Individually evaluated for impairment	118	267
Allowance for loan losses: Amounts related to purchased credit impaired loans	646	1,271
Allowance for loan losses: Collectively evaluated for impairment	29,739	24,604
Loans: Individually evaluated for impairment	1,292	2,154
Loans: Purchased credit impaired loans	6,178	11,033
Loans: Collectively evaluated for impairment	2,107,825	2,046,744
Loans receivable	2,115,295	2,059,931
Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(527)	(378)
Allowance for loan losses: Recoveries	704	972
Allowance for loan losses: Net provision for loan losses	(1,897)	(1,404)
Allowance for loan losses: (Decrease) increase in FDIC loss share receivable	(2,526)	(3,957)
Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs		(1)
Allowance for loan losses: Recoveries	1	2
Allowance for loan losses: Net provision for loan losses	(213)	(462)
Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(77)	(18)
Allowance for loan losses: Recoveries	144	361
Allowance for loan losses: Net provision for loan losses	(301)	(594)
Purchased Credit Impaired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(297)	(323)
Allowance for loan losses: Recoveries	24	36
Allowance for loan losses: Net provision for loan losses	(168)	1,876
Allowance for loan losses: (Decrease) increase in FDIC loss share receivable	(2,344)	(4,209)
Purchased Credit Impaired Loans [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(153)	(8)
Allowance for loan losses: Recoveries	75	189
Allowance for loan losses: Net provision for loan losses	(412)	(1,740)
Allowance for loan losses: (Decrease) increase in FDIC loss share receivable	(135)	283
Non-Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(86,734)	(72,888)
Allowance for loan losses: Recoveries	18,005	13,831
Allowance for loan losses: Net provision for loan losses	60,865	112,063
Non-Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(259)	(346)
Allowance for loan losses: Recoveries	987	989
Allowance for loan losses: Net provision for loan losses	(316)	7,286
Non-Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(619)	(964)
Allowance for loan losses: Recoveries	1,459	1,725
Allowance for loan losses: Net provision for loan losses	495	119
Non-Purchased Credit Impaired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(2,542)	(1,040)
Allowance for loan losses: Recoveries	1,040	859
Allowance for loan losses: Net provision for loan losses	3,770	2,809
Non-Purchased Credit Impaired Loans [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(31,277)	(26,099)
Allowance for loan losses: Recoveries	6,605	5,809
Allowance for loan losses: Net provision for loan losses	29,658	22,851
Total Commercial And Industrial [Member] | Total Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	158,135	119,286
Allowance for loan losses: Ending balance	140,880	158,135	119,286
Allowance for loan losses: Individually evaluated for impairment	16,922	28,433
Allowance for loan losses: Amounts related to purchased credit impaired loans	990	1,380
Allowance for loan losses: Collectively evaluated for impairment	122,968	128,322
Loans: Individually evaluated for impairment	289,372	277,530
Loans: Purchased credit impaired loans	13,235	24,691
Loans: Collectively evaluated for impairment	10,137,769	9,218,517
Loans receivable	10,440,376	9,520,738
Total Commercial And Industrial [Member] | Total Commercial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	147,052	109,428
Allowance for loan losses: Ending balance	127,918	147,052	109,428
Allowance for loan losses: Individually evaluated for impairment	16,129	28,187
Allowance for loan losses: Amounts related to purchased credit impaired loans	525	486
Allowance for loan losses: Collectively evaluated for impairment	111,264	118,379
Loans: Individually evaluated for impairment	267,881	271,262
Loans: Purchased credit impaired loans	5,941	11,368
Loans: Collectively evaluated for impairment	8,024,115	7,331,287
Loans receivable	8,297,937	7,613,917
Total Commercial And Industrial [Member] | Total Commercial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	11,083	9,858
Allowance for loan losses: Ending balance	12,962	11,083	$ 9,858
Allowance for loan losses: Individually evaluated for impairment	793	246
Allowance for loan losses: Amounts related to purchased credit impaired loans	465	894
Allowance for loan losses: Collectively evaluated for impairment	11,704	9,943
Loans: Individually evaluated for impairment	21,491	6,268
Loans: Purchased credit impaired loans	7,294	13,323
Loans: Collectively evaluated for impairment	2,113,654	1,887,230
Loans receivable	2,142,439	1,906,821
Total Commercial And Industrial [Member] | Purchased Credit Impaired Loans [Member] | Total Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs		(28)
Allowance for loan losses: Recoveries	460	384
Allowance for loan losses: Net provision for loan losses	(803)	(484)
Allowance for loan losses: (Decrease) increase in FDIC loss share receivable	(47)	(31)
Total Commercial And Industrial [Member] | Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Recoveries	7	115
Allowance for loan losses: Net provision for loan losses	79	(44)
Allowance for loan losses: (Decrease) increase in FDIC loss share receivable	(47)	(31)
Total Commercial And Industrial [Member] | Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs		(28)
Allowance for loan losses: Recoveries	453	269
Allowance for loan losses: Net provision for loan losses	(882)	(440)
Total Commercial And Industrial [Member] | Non-Purchased Credit Impaired Loans [Member] | Total Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(52,037)	(44,439)
Allowance for loan losses: Recoveries	7,914	4,449
Allowance for loan losses: Net provision for loan losses	27,258	78,998
Total Commercial And Industrial [Member] | Non-Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(51,479)	(42,620)
Allowance for loan losses: Recoveries	7,519	3,969
Allowance for loan losses: Net provision for loan losses	24,787	76,235
Total Commercial And Industrial [Member] | Non-Purchased Credit Impaired Loans [Member] | Total Commercial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(558)	(1,819)
Allowance for loan losses: Recoveries	395	480
Allowance for loan losses: Net provision for loan losses	$ 2,471	$ 2,763