Loans - Commercial Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	$ 13,273,392	$ 12,990,779
Originated
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	7,959,769	7,458,401
Originated | Commercial
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,989,609	1,901,526
Originated | Commercial real estate
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	2,114,540	1,921,799
Originated | Real estate construction and land development
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	327,740	281,724
Acquired
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	5,313,623	5,532,378
Commercial loan portfolio
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	7,805,190	7,594,212
Commercial loan portfolio | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	7,404,839	7,167,397
Commercial loan portfolio | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	165,269	192,013
Commercial loan portfolio | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	234,881	233,479
Commercial loan portfolio | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	201	1,323
Commercial loan portfolio | Commercial
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	3,253,608	3,217,300
Commercial loan portfolio | Commercial real estate
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	4,097,771	3,973,140
Commercial loan portfolio | Real estate construction and land development
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	453,811	403,772
Commercial loan portfolio | Originated
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	4,431,889	4,105,049
Commercial loan portfolio | Originated | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	4,269,870	3,934,033
Commercial loan portfolio | Originated | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	72,265	81,947
Commercial loan portfolio | Originated | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	89,753	87,999
Commercial loan portfolio | Originated | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1	1,070
Commercial loan portfolio | Originated | Commercial
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,989,609	1,901,526
Commercial loan portfolio | Originated | Commercial | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,902,773	1,803,750
Commercial loan portfolio | Originated | Commercial | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	34,018	44,809
Commercial loan portfolio | Originated | Commercial | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	52,818	51,898
Commercial loan portfolio | Originated | Commercial | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	0	1,069
Commercial loan portfolio | Originated | Commercial real estate
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	2,114,540	1,921,799
Commercial loan portfolio | Originated | Commercial real estate | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	2,040,155	1,849,315
Commercial loan portfolio | Originated | Commercial real estate | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	37,528	36,981
Commercial loan portfolio | Originated | Commercial real estate | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	36,856	35,502
Commercial loan portfolio | Originated | Commercial real estate | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1	1
Commercial loan portfolio | Originated | Real estate construction and land development
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	327,740	281,724
Commercial loan portfolio | Originated | Real estate construction and land development | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	326,942	280,968
Commercial loan portfolio | Originated | Real estate construction and land development | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	719	157
Commercial loan portfolio | Originated | Real estate construction and land development | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	79	599
Commercial loan portfolio | Originated | Real estate construction and land development | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	0	0
Commercial loan portfolio | Acquired
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	3,373,301	3,489,163
Commercial loan portfolio | Acquired | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	3,134,969	3,233,364
Commercial loan portfolio | Acquired | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	93,004	110,066
Commercial loan portfolio | Acquired | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	145,128	145,480
Commercial loan portfolio | Acquired | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	200	253
Commercial loan portfolio | Acquired | Commercial
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,263,999	1,315,774
Commercial loan portfolio | Acquired | Commercial | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,171,260	1,218,848
Commercial loan portfolio | Acquired | Commercial | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	39,079	46,643
Commercial loan portfolio | Acquired | Commercial | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	53,625	50,283
Commercial loan portfolio | Acquired | Commercial | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	35	0
Commercial loan portfolio | Acquired | Commercial real estate
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,983,231	2,051,341
Commercial loan portfolio | Acquired | Commercial real estate | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,841,116	1,897,011
Commercial loan portfolio | Acquired | Commercial real estate | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	52,038	61,441
Commercial loan portfolio | Acquired | Commercial real estate | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	89,912	92,636
Commercial loan portfolio | Acquired | Commercial real estate | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	165	253
Commercial loan portfolio | Acquired | Real estate construction and land development
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	126,071	122,048
Commercial loan portfolio | Acquired | Real estate construction and land development | Pass
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	122,593	117,505
Commercial loan portfolio | Acquired | Real estate construction and land development | Special Mention
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,887	1,982
Commercial loan portfolio | Acquired | Real estate construction and land development | Substandard
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	1,591	2,561
Commercial loan portfolio | Acquired | Real estate construction and land development | Doubtful
Recorded investment of loans in commercial loan portfolio by risk rating categories
Total loans	$ 0	$ 0