Loans (Summary of Recorded Investment of Commercial Loans by Risk Rating Categories) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 14,155,267	$ 12,990,779
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans		3,217,300
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans		3,973,140
Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans		403,772
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	8,460,527	7,594,212
Commercial Portfolio Segment [Member] | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,038,463	7,167,397
Commercial Portfolio Segment [Member] | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	204,706	192,013
Commercial Portfolio Segment [Member] | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	216,353	233,479
Commercial Portfolio Segment [Member] | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	1,005	1,323
Commercial Portfolio Segment [Member] | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	3,385,642
Commercial Portfolio Segment [Member] | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	4,500,670
Commercial Portfolio Segment [Member] | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	574,215
Commercial Originated Portfolio
Financing Receivable, Recorded Investment [Line Items]
Loans	5,657,186	4,105,049
Commercial Originated Portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,488,571	3,934,033
Commercial Originated Portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	66,100	81,947
Commercial Originated Portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	102,515	87,999
Commercial Originated Portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1,070
Commercial Originated Portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	2,407,606	1,901,526
Commercial Originated Portfolio | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,316,464	1,803,750
Commercial Originated Portfolio | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	41,059	44,809
Commercial Originated Portfolio | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	50,083	51,898
Commercial Originated Portfolio | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1,069
Commercial Originated Portfolio | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,751,425	1,921,799
Commercial Originated Portfolio | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,677,579	1,849,315
Commercial Originated Portfolio | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	24,204	36,981
Commercial Originated Portfolio | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	49,642	35,502
Commercial Originated Portfolio | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	1
Commercial Originated Portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	498,155	281,724
Commercial Originated Portfolio | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	494,528	280,968
Commercial Originated Portfolio | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	837	157
Commercial Originated Portfolio | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	2,790	599
Commercial Originated Portfolio | Real estate construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial Acquired Portfolio
Financing Receivable, Recorded Investment [Line Items]
Loans	2,803,341	3,489,163
Commercial Acquired Portfolio | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	2,549,892	3,233,364
Commercial Acquired Portfolio | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	138,606	110,066
Commercial Acquired Portfolio | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	113,838	145,480
Commercial Acquired Portfolio | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	1,005	253
Commercial Acquired Portfolio | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	978,036	1,315,774
Commercial Acquired Portfolio | Commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	873,861	1,218,848
Commercial Acquired Portfolio | Commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	68,418	46,643
Commercial Acquired Portfolio | Commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	35,539	50,283
Commercial Acquired Portfolio | Commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	218	0
Commercial Acquired Portfolio | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,749,245	2,051,341
Commercial Acquired Portfolio | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,603,685	1,897,011
Commercial Acquired Portfolio | Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	67,970	61,441
Commercial Acquired Portfolio | Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	76,803	92,636
Commercial Acquired Portfolio | Commercial real estate | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	787	253
Commercial Acquired Portfolio | Real estate construction and land development
Financing Receivable, Recorded Investment [Line Items]
Loans	76,060	122,048
Commercial Acquired Portfolio | Real estate construction and land development | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	72,346	117,505
Commercial Acquired Portfolio | Real estate construction and land development | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	2,218	1,982
Commercial Acquired Portfolio | Real estate construction and land development | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	1,496	2,561
Commercial Acquired Portfolio | Real estate construction and land development | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	$ 0