Loans and Allowance for Loan Losses (Allowance for Loan Losses by Portfolio Class) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	$ 217,308	$ 229,418
Allowance for loan losses: Net provision for loan losses	12,253	15,991
Allowance for loan losses: Decrease in FDIC loss share receivable		(1,830)
Allowance for loan losses: Ending balance	210,713	213,550
Allowance for loan losses: Individually evaluated for impairment	24,601	16,501
Allowance for loan losses: Amounts related to purchased credit impaired loans	14,047	15,999
Allowance for loan losses: Collectively evaluated for impairment	172,065	181,050
Loans: Individually evaluated for impairment	377,370	256,458
Loans: Purchased credit impaired loans	149,383	179,367
Loans: Collectively evaluated for impairment	18,565,751	17,769,043
Loans receivable	19,092,504	18,204,868	$ 19,004,163
Total Commercial [Member] \| Commercial Real Estate - Income Producing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	13,709	13,509
Allowance for loan losses: Decrease in FDIC loss share receivable
Allowance for loan losses: Ending balance	12,985	13,611
Allowance for loan losses: Individually evaluated for impairment	1,261	1,114
Allowance for loan losses: Amounts related to purchased credit impaired loans	576	213
Allowance for loan losses: Collectively evaluated for impairment	11,148	12,284
Loans: Individually evaluated for impairment	14,071	13,599
Loans: Purchased credit impaired loans	4,361	7,669
Loans: Collectively evaluated for impairment	2,376,430	2,483,836
Loans receivable	2,394,862	2,505,104	2,384,599
Total Commercial [Member] \| Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	7,372	6,271
Allowance for loan losses: Decrease in FDIC loss share receivable
Allowance for loan losses: Ending balance	9,924	6,720
Allowance for loan losses: Individually evaluated for impairment	1	1
Allowance for loan losses: Amounts related to purchased credit impaired loans	173	283
Allowance for loan losses: Collectively evaluated for impairment	9,750	6,436
Loans: Individually evaluated for impairment	113	1,592
Loans: Purchased credit impaired loans	5,843	4,326
Loans: Collectively evaluated for impairment	1,407,922	1,246,749
Loans receivable	1,413,878	1,252,667	1,373,421
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	24,844	25,361
Allowance for loan losses: Decrease in FDIC loss share receivable		(1,696)
Allowance for loan losses: Ending balance	24,918	23,806
Allowance for loan losses: Individually evaluated for impairment	276	94
Allowance for loan losses: Amounts related to purchased credit impaired loans	11,720	13,286
Allowance for loan losses: Collectively evaluated for impairment	12,922	10,426
Loans: Individually evaluated for impairment	8,338	3,236
Loans: Purchased credit impaired loans	116,409	138,260
Loans: Collectively evaluated for impairment	2,608,074	2,124,767
Loans receivable	2,732,821	2,266,263	2,690,472
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	30,503	26,142
Allowance for loan losses: Decrease in FDIC loss share receivable		(103)
Allowance for loan losses: Ending balance	22,660	26,622
Allowance for loan losses: Individually evaluated for impairment	232	199
Allowance for loan losses: Amounts related to purchased credit impaired loans	612	1,019
Allowance for loan losses: Collectively evaluated for impairment	21,816	25,404
Loans: Individually evaluated for impairment	617	2,149
Loans: Purchased credit impaired loans	5,876	9,951
Loans: Collectively evaluated for impairment	2,022,685	2,046,996
Loans receivable	2,029,178	2,059,096	2,115,295
Non-Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(18,436)	(33,944)
Allowance for loan losses: Recoveries	6,236	3,915
Allowance for loan losses: Net provision for loan losses	12,253	15,991
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		(7)
Allowance for loan losses: Recoveries	63	375
Allowance for loan losses: Net provision for loan losses	(787)	(266)
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	(10)	(91)
Allowance for loan losses: Recoveries	29	471
Allowance for loan losses: Net provision for loan losses	2,533	69
Non-Purchased Credit Impaired Loans [Member] \| Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(192)	(348)
Allowance for loan losses: Recoveries	116	113
Allowance for loan losses: Net provision for loan losses	150	376
Non-Purchased Credit Impaired Loans [Member] \| Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Charge-offs	(8,048)	(8,678)
Allowance for loan losses: Recoveries	1,794	1,743
Allowance for loan losses: Net provision for loan losses	5,059	7,518
Total Commercial And Industrial [Member] \| Total Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses: Beginning balance	140,880	158,135
Allowance for loan losses: Decrease in FDIC loss share receivable		(31)
Allowance for loan losses: Ending balance	140,226	142,791
Allowance for loan losses: Individually evaluated for impairment	22,831	15,093
Allowance for loan losses: Amounts related to purchased credit impaired loans	966	1,198
Allowance for loan losses: Collectively evaluated for impairment	116,429	126,500
Loans: Individually evaluated for impairment	354,231	235,882
Loans: Purchased credit impaired loans	16,894	19,161
Loans: Collectively evaluated for impairment	10,150,640	9,866,695
Loans receivable	10,521,765	10,121,738	10,440,376
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	127,918	147,052
Allowance for loan losses: Decrease in FDIC loss share receivable		(31)
Allowance for loan losses: Ending balance	126,606	131,269
Allowance for loan losses: Individually evaluated for impairment	20,356	15,017
Allowance for loan losses: Amounts related to purchased credit impaired loans	471	411
Allowance for loan losses: Collectively evaluated for impairment	105,779	115,841
Loans: Individually evaluated for impairment	323,913	231,988
Loans: Purchased credit impaired loans	8,510	6,693
Loans: Collectively evaluated for impairment	8,003,799	7,835,606
Loans receivable	8,336,222	8,074,287	8,297,937
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	12,962	11,083
Allowance for loan losses: Decrease in FDIC loss share receivable
Allowance for loan losses: Ending balance	13,620	11,522
Allowance for loan losses: Individually evaluated for impairment	2,475	76
Allowance for loan losses: Amounts related to purchased credit impaired loans	495	787
Allowance for loan losses: Collectively evaluated for impairment	10,650	10,659
Loans: Individually evaluated for impairment	30,318	3,894
Loans: Purchased credit impaired loans	8,384	12,468
Loans: Collectively evaluated for impairment	2,146,841	2,031,089
Loans receivable	2,185,543	2,047,451	$ 2,142,439
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	(10,186)	(24,820)
Allowance for loan losses: Recoveries	4,234	1,213
Allowance for loan losses: Net provision for loan losses	5,298	8,294
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	(9,335)	(24,791)
Allowance for loan losses: Recoveries	4,146	938
Allowance for loan losses: Net provision for loan losses	3,877	8,101
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	(851)	(29)
Allowance for loan losses: Recoveries	88	275
Allowance for loan losses: Net provision for loan losses	$ 1,421	$ 193

Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
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The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Change in carrying amount of the indemnification asset relating to loss sharing agreements with the Federal Deposit Insurance Corporation (FDIC). The change includes for example, but is not limited to, acquisitions, additional estimated losses, disposals, cash payments, accretion of discount and write-offs, net of recoveries.

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A valuation allowance for financing receivables that are expected to be uncollectible.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of direct write-downs of financing receivables charged against the allowance.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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