Loans and Allowance for Loan Losses - (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Loans and Allowance for Loan Losses
Loans, net	$ 10,855,344		$ 10,575,417	$ 8,223,204
Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	7,606,478		6,492,155	6,230,327
Less allowance for non-acquired loan losses	(49,869)	$ (47,874)	(43,448)	(41,541)	$ (40,149)	$ (36,960)
Loans, net	7,556,609		6,448,707	6,188,786
Acquired credit impaired loans
Loans and Allowance for Loan Losses
Total loans	516,601		623,430	582,533
Acquired non-credit impaired loans
Loans and Allowance for Loan Losses
Total loans	2,786,102		3,507,907	1,455,555
Residential real estate | Acquired credit impaired loans
Loans and Allowance for Loan Losses
Total loans	218,019		260,787	249,666
Commercial non-owner occupied real estate | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	2,182,164		1,839,768	1,716,827
Commercial non-owner occupied real estate | Non-acquired loans | Construction and land development
Loans and Allowance for Loan Losses
Total loans	902,836		830,875	766,957
Less allowance for non-acquired loan losses	(6,013)	(6,187)	(5,921)	(5,972)	(5,746)	(4,091)
Commercial non-owner occupied real estate | Non-acquired loans | Other commercial non-owner occupied real estate
Loans and Allowance for Loan Losses
Total loans	1,279,328		1,008,893	949,870
Less allowance for non-acquired loan losses	(7,985)	(7,209)	(6,525)	(6,237)	(6,164)	(4,980)
Commercial non-owner occupied real estate | Acquired credit impaired loans | Construction and land development
Loans and Allowance for Loan Losses
Total loans	34,312		49,649	46,248
Commercial non-owner occupied real estate | Acquired credit impaired loans | Other commercial non-owner occupied real estate
Loans and Allowance for Loan Losses
Total loans	209,518		234,595	207,521
Commercial non-owner occupied real estate | Acquired non-credit impaired loans | Construction and land development
Loans and Allowance for Loan Losses
Total loans	222,562		403,357	76,886
Commercial non-owner occupied real estate | Acquired non-credit impaired loans | Other commercial non-owner occupied real estate
Loans and Allowance for Loan Losses
Total loans	684,793		817,166	199,704
Commercial owner occupied real estate loan | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	1,449,069		1,262,776	1,278,487
Less allowance for non-acquired loan losses	(9,077)	(8,607)	(8,128)	(8,110)	(7,539)	(8,022)
Commercial owner occupied real estate loan | Non-acquired loans | Home equity loans
Loans and Allowance for Loan Losses
Less allowance for non-acquired loan losses	(3,441)		(3,250)	(3,097)		(3,211)
Commercial owner occupied real estate loan | Acquired non-credit impaired loans
Loans and Allowance for Loan Losses
Total loans	455,803		521,818	207,572
Consumer loans | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	2,317,584		1,967,902	1,874,518
Consumer loans | Non-acquired loans | Home equity loans
Loans and Allowance for Loan Losses
Total loans	473,381		437,642	419,760
Less allowance for non-acquired loan losses	(3,441)	(3,368)		(3,097)	(3,247)
Consumer loans | Non-acquired loans | Consumer Owner Occupied Loans
Loans and Allowance for Loan Losses
Total loans	1,844,203		1,530,260	1,454,758
Less allowance for non-acquired loan losses	(11,380)	(10,945)	(9,668)	(9,126)	(8,569)	(7,820)
Consumer loans | Acquired non-credit impaired loans | Home equity loans
Loans and Allowance for Loan Losses
Total loans	259,558		320,591	164,291
Consumer loans | Acquired non-credit impaired loans | Consumer Owner Occupied Loans
Loans and Allowance for Loan Losses
Total loans	647,064		710,611	492,615
Commercial and industrial | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	991,842		815,187	781,757
Less allowance for non-acquired loan losses	(6,923)	(6,711)	(5,488)	(5,203)	(5,143)	(4,842)
Commercial and industrial | Acquired credit impaired loans
Loans and Allowance for Loan Losses
Total loans	10,671		26,946	25,796
Commercial and industrial | Acquired non-credit impaired loans
Loans and Allowance for Loan Losses
Total loans	247,922		398,696	101,427
Other income producing property | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	209,983		193,847	194,335
Less allowance for non-acquired loan losses	(1,410)	(1,413)	(1,375)	(1,388)	(1,379)	(1,542)
Other income producing property | Acquired non-credit impaired loans
Loans and Allowance for Loan Losses
Total loans	150,371		196,669	76,924
Consumer | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	438,789		378,985	371,758
Less allowance for non-acquired loan losses	(3,183)	(3,071)	(2,788)	(2,692)	(2,532)	(2,350)
Consumer | Non-acquired loans | Consumer
Loans and Allowance for Loan Losses
Total loans	438,789		378,985	371,758
Consumer | Acquired credit impaired loans
Loans and Allowance for Loan Losses
Total loans	44,081		51,453	53,302
Consumer | Acquired non-credit impaired loans
Loans and Allowance for Loan Losses
Total loans	118,029		137,710	136,136
Commercial loans | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	4,833,058		4,111,578	3,971,406
Other loans | Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	17,047		33,690	12,645
Less allowance for non-acquired loan losses	$ (457)	$ (363)	(305)	$ 284	$ 170	$ (102)
Other loans | Acquired non-credit impaired loans
Loans and Allowance for Loan Losses
Total loans			$ 1,289