Loans and Allowance for Loan Losses (Allowance for Loan Losses by Portfolio Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 181,179	$ 128,762
Allowance for loan losses: Charge-offs	(24,740)	(10,464)
Allowance for loan losses: Recoveries	3,508	4,355
Allowance for loan losses: Net provision for loan losses	60,036	6,154
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(2,189)	(421)
Allowance for loan losses: Ending balance	217,794	128,386
Allowance for loan losses: Individually evaluated for impairment	28,167	1,092
Allowance for loan losses: Amounts related to acquired-impaired loans	20,502	27,638
Allowance for loan losses: Collectively evaluated for impairment	169,125	99,656
Ending balance: Loans	15,978,124	13,924,386	$ 15,703,314
Loans: Individually evaluated for impairment	230,741	41,279
Loans: Acquired-impaired loans	221,893	283,777
Loans: Collectively evaluated for impairment	15,525,490	13,599,330
Originated Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	158,026	97,701
Allowance for loan losses: Charge-offs	(24,693)	(7,460)
Allowance for loan losses: Recoveries	3,394	3,806
Allowance for loan losses: Net provision for loan losses	60,558	6,447
Allowance for loan losses: Ending balance	197,285	100,494
Allowance for loan losses: Individually evaluated for impairment	28,160	838
Allowance for loan losses: Collectively evaluated for impairment	169,125	99,656
Ending balance: Loans	15,567,288	12,920,530	15,258,587
Loans: Individually evaluated for impairment	228,435	38,700
Loans: Collectively evaluated for impairment	15,338,853	12,881,830
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 33	$ 477
Allowance for loan losses: Charge-offs
Allowance for loan losses: Recoveries
Allowance for loan losses: Net provision for loan losses	$ (26)	$ (223)
Allowance for loan losses: Ending balance	7	254
Allowance for loan losses: Individually evaluated for impairment	$ 7	$ 254
Allowance for loan losses: Amounts related to acquired-impaired loans
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 211,620	$ 765,324	241,430
Loans: Individually evaluated for impairment	2,306	2,579
Loans: Acquired-impaired loans	22,677	45,245	22,541	$ 61,276
Loans: Collectively evaluated for impairment	186,637	717,500
FDIC Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	23,120	30,584
Allowance for loan losses: Charge-offs	(47)	(3,004)
Allowance for loan losses: Recoveries	114	549
Allowance for loan losses: Net provision for loan losses	(496)	(70)
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(2,189)	(421)
Allowance for loan losses: Ending balance	$ 20,502	$ 27,638
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans	$ 20,502	$ 27,638
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 199,216	$ 238,532	203,297
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 199,216	$ 238,532	203,297	$ 252,409
Loans: Collectively evaluated for impairment
Commercial Non-Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 109,428	$ 51,169
Allowance for loan losses: Charge-offs	(17,667)	(1,824)
Allowance for loan losses: Recoveries	812	995
Allowance for loan losses: Net provision for loan losses	52,103	6,752
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(17)	(13)
Allowance for loan losses: Ending balance	144,659	57,079
Allowance for loan losses: Individually evaluated for impairment	26,502	529
Allowance for loan losses: Amounts related to acquired-impaired loans	439	783
Allowance for loan losses: Collectively evaluated for impairment	117,718	55,767
Ending balance: Loans	7,145,406	5,987,084	6,995,824
Loans: Individually evaluated for impairment	201,029	14,566
Loans: Acquired-impaired loans	12,659	15,645
Loans: Collectively evaluated for impairment	6,931,718	5,956,873
Commercial Non-Real Estate [Member] | Originated Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	108,982	50,258
Allowance for loan losses: Charge-offs	(17,667)	(1,697)
Allowance for loan losses: Recoveries	809	981
Allowance for loan losses: Net provision for loan losses	52,096	6,754
Allowance for loan losses: Ending balance	144,220	56,296
Allowance for loan losses: Individually evaluated for impairment	26,502	529
Allowance for loan losses: Collectively evaluated for impairment	117,718	55,767
Ending balance: Loans	7,088,146	5,861,887	6,930,453
Loans: Individually evaluated for impairment	201,029	14,566
Loans: Collectively evaluated for impairment	$ 6,887,117	$ 5,847,321
Commercial Non-Real Estate [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance
Allowance for loan losses: Charge-offs
Allowance for loan losses: Recoveries
Allowance for loan losses: Net provision for loan losses
Allowance for loan losses: Ending balance
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 51,949	$ 118,260	59,843
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 7,348	$ 8,708
Loans: Collectively evaluated for impairment	44,601	109,552
Commercial Non-Real Estate [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 446	911
Allowance for loan losses: Charge-offs		(127)
Allowance for loan losses: Recoveries	$ 3	14
Allowance for loan losses: Net provision for loan losses	7	(2)
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(17)	(13)
Allowance for loan losses: Ending balance	$ 439	$ 783
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans	$ 439	$ 783
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 5,311	$ 6,937	5,528
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 5,311	$ 6,937
Loans: Collectively evaluated for impairment
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 15,899	$ 21,082
Allowance for loan losses: Charge-offs	(927)	(2,619)
Allowance for loan losses: Recoveries	221	110
Allowance for loan losses: Net provision for loan losses	$ 6,996	(987)
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable		1,207
Allowance for loan losses: Ending balance	$ 22,189	18,793
Allowance for loan losses: Individually evaluated for impairment	1,339	401
Allowance for loan losses: Amounts related to acquired-impaired loans	1,511	3,215
Allowance for loan losses: Collectively evaluated for impairment	19,339	15,177
Ending balance: Loans	3,676,092	3,150,103	3,412,551
Loans: Individually evaluated for impairment	14,699	19,789
Loans: Acquired-impaired loans	27,049	49,003
Loans: Collectively evaluated for impairment	3,634,344	3,081,311
Commercial Real Estate [Member] | Originated Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	14,059	16,544
Allowance for loan losses: Charge-offs	(898)	(251)
Allowance for loan losses: Recoveries	185	(3)
Allowance for loan losses: Net provision for loan losses	7,325	(966)
Allowance for loan losses: Ending balance	20,671	15,324
Allowance for loan losses: Individually evaluated for impairment	1,332	147
Allowance for loan losses: Collectively evaluated for impairment	19,339	15,177
Ending balance: Loans	3,504,803	2,492,351	3,220,509
Loans: Individually evaluated for impairment	12,393	17,210
Loans: Collectively evaluated for impairment	3,492,410	2,475,141
Commercial Real Estate [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 33	$ 477
Allowance for loan losses: Charge-offs
Allowance for loan losses: Recoveries
Allowance for loan losses: Net provision for loan losses	$ (26)	$ (223)
Allowance for loan losses: Ending balance	7	254
Allowance for loan losses: Individually evaluated for impairment	$ 7	$ 254
Allowance for loan losses: Amounts related to acquired-impaired loans
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 156,285	$ 629,975	176,460
Loans: Individually evaluated for impairment	2,306	2,579
Loans: Acquired-impaired loans	12,045	21,226
Loans: Collectively evaluated for impairment	141,934	606,170
Commercial Real Estate [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	1,807	4,061
Allowance for loan losses: Charge-offs	(29)	(2,368)
Allowance for loan losses: Recoveries	36	113
Allowance for loan losses: Net provision for loan losses	$ (303)	202
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable		1,207
Allowance for loan losses: Ending balance	$ 1,511	$ 3,215
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans	$ 1,511	$ 3,215
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 15,004	$ 27,777	15,582
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 15,004	$ 27,777
Loans: Collectively evaluated for impairment
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 25,353	$ 28,660
Allowance for loan losses: Charge-offs	(175)	(1,302)
Allowance for loan losses: Recoveries	302	305
Allowance for loan losses: Net provision for loan losses	1,365	543
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(2,153)	(1,171)
Allowance for loan losses: Ending balance	24,692	27,035
Allowance for loan losses: Individually evaluated for impairment	125	88
Allowance for loan losses: Amounts related to acquired-impaired loans	16,641	19,150
Allowance for loan losses: Collectively evaluated for impairment	7,926	7,797
Ending balance: Loans	2,000,967	1,913,885	2,049,524
Loans: Individually evaluated for impairment	883	2,423
Loans: Acquired-impaired loans	161,078	177,852
Loans: Collectively evaluated for impairment	1,839,006	1,733,610
Residential Mortgages [Member] | Originated Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	7,690	8,051
Allowance for loan losses: Charge-offs	(175)	(1,209)
Allowance for loan losses: Recoveries	301	305
Allowance for loan losses: Net provision for loan losses	235	738
Allowance for loan losses: Ending balance	8,051	7,885
Allowance for loan losses: Individually evaluated for impairment	125	88
Allowance for loan losses: Collectively evaluated for impairment	7,926	7,797
Ending balance: Loans	1,839,889	1,736,033	1,887,256
Loans: Individually evaluated for impairment	883	2,423
Loans: Collectively evaluated for impairment	$ 1,839,006	$ 1,733,610
Residential Mortgages [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance
Allowance for loan losses: Charge-offs
Allowance for loan losses: Recoveries
Allowance for loan losses: Net provision for loan losses
Allowance for loan losses: Ending balance
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 1,116	$ 2,485	27
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 1,116	$ 2,485
Loans: Collectively evaluated for impairment
Residential Mortgages [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 17,663	$ 20,609
Allowance for loan losses: Charge-offs		$ (93)
Allowance for loan losses: Recoveries	$ 1
Allowance for loan losses: Net provision for loan losses	1,130	$ (195)
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(2,153)	(1,171)
Allowance for loan losses: Ending balance	$ 16,641	$ 19,150
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans	$ 16,641	$ 19,150
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 159,962	$ 175,367	162,241
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 159,962	$ 175,367
Loans: Collectively evaluated for impairment
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 24,857	$ 21,430
Allowance for loan losses: Charge-offs	(5,843)	(3,696)
Allowance for loan losses: Recoveries	1,533	1,296
Allowance for loan losses: Net provision for loan losses	1,350	1,352
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(19)	(410)
Allowance for loan losses: Ending balance	21,878	19,972
Allowance for loan losses: Individually evaluated for impairment	16	3
Allowance for loan losses: Amounts related to acquired-impaired loans	1,388	3,392
Allowance for loan losses: Collectively evaluated for impairment	20,474	16,577
Ending balance: Loans	2,060,245	1,759,804	2,093,465
Loans: Individually evaluated for impairment	58	120
Loans: Acquired-impaired loans	12,177	16,994
Loans: Collectively evaluated for impairment	2,048,010	1,742,690
Consumer [Member] | Originated Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	22,310	17,435
Allowance for loan losses: Charge-offs	(5,843)	(3,556)
Allowance for loan losses: Recoveries	1,494	1,280
Allowance for loan losses: Net provision for loan losses	2,529	1,421
Allowance for loan losses: Ending balance	20,490	16,580
Allowance for loan losses: Individually evaluated for impairment	16	3
Allowance for loan losses: Collectively evaluated for impairment	20,474	16,577
Ending balance: Loans	2,048,068	1,742,810	2,080,626
Loans: Individually evaluated for impairment	58	120
Loans: Collectively evaluated for impairment	$ 2,048,010	$ 1,742,690
Consumer [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance
Allowance for loan losses: Charge-offs
Allowance for loan losses: Recoveries
Allowance for loan losses: Net provision for loan losses
Allowance for loan losses: Ending balance
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 20	$ 25	20
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 20	$ 25
Loans: Collectively evaluated for impairment
Consumer [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 2,547	$ 3,995
Allowance for loan losses: Charge-offs		(140)
Allowance for loan losses: Recoveries	$ 39	16
Allowance for loan losses: Net provision for loan losses	(1,179)	(69)
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable	(19)	(410)
Allowance for loan losses: Ending balance	$ 1,388	$ 3,392
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans	$ 1,388	$ 3,392
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 12,157	$ 16,969	12,819
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 12,157	$ 16,969
Loans: Collectively evaluated for impairment
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 5,642	$ 6,421
Allowance for loan losses: Charge-offs	(128)	(1,023)
Allowance for loan losses: Recoveries	640	1,649
Allowance for loan losses: Net provision for loan losses	$ (1,778)	(1,506)
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable		(34)
Allowance for loan losses: Ending balance	$ 4,376	5,507
Allowance for loan losses: Individually evaluated for impairment	185	71
Allowance for loan losses: Amounts related to acquired-impaired loans	523	1,098
Allowance for loan losses: Collectively evaluated for impairment	3,668	4,338
Ending balance: Loans	1,095,414	1,113,510	1,151,950
Loans: Individually evaluated for impairment	14,072	4,381
Loans: Acquired-impaired loans	8,930	24,283
Loans: Collectively evaluated for impairment	1,072,412	1,084,846
Construction and Land Development [Member] | Originated Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	4,985	5,413
Allowance for loan losses: Charge-offs	(110)	(747)
Allowance for loan losses: Recoveries	605	1,243
Allowance for loan losses: Net provision for loan losses	(1,627)	(1,500)
Allowance for loan losses: Ending balance	3,853	4,409
Allowance for loan losses: Individually evaluated for impairment	185	71
Allowance for loan losses: Collectively evaluated for impairment	3,668	4,338
Ending balance: Loans	1,086,382	1,087,449	1,139,743
Loans: Individually evaluated for impairment	14,072	4,381
Loans: Collectively evaluated for impairment	$ 1,072,310	$ 1,083,068
Construction and Land Development [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance
Allowance for loan losses: Charge-offs
Allowance for loan losses: Recoveries
Allowance for loan losses: Net provision for loan losses
Allowance for loan losses: Ending balance
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 2,250	$ 14,579	5,080
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 2,148	$ 12,801
Loans: Collectively evaluated for impairment	102	1,778
Construction and Land Development [Member] | FDIC Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	657	1,008
Allowance for loan losses: Charge-offs	(18)	(276)
Allowance for loan losses: Recoveries	35	406
Allowance for loan losses: Net provision for loan losses	$ (151)	(6)
Allowance for loan losses: Increase (decrease) in FDIC loss share receivable		(34)
Allowance for loan losses: Ending balance	$ 523	$ 1,098
Allowance for loan losses: Individually evaluated for impairment
Allowance for loan losses: Amounts related to acquired-impaired loans	$ 523	$ 1,098
Allowance for loan losses: Collectively evaluated for impairment
Ending balance: Loans	$ 6,782	$ 11,482	$ 7,127
Loans: Individually evaluated for impairment
Loans: Acquired-impaired loans	$ 6,782	$ 11,482
Loans: Collectively evaluated for impairment