Loans and Allowance for Loan Losses - Credit risk profile by risk grade of non acquired loans - (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Loans and Allowance for Loan Losses
Other Real Estate, Non Covered	$ 22,211	$ 4,200	$ 24,803	$ 25,913	$ 26,499
Non-acquired loans
Loans and Allowance for Loan Losses
Total loans	5,008,113		4,220,726	3,994,716
Non-acquired loans | Pass
Loans and Allowance for Loan Losses
Total loans	4,873,202		4,077,013	3,843,597
Non-acquired loans | Special mention
Loans and Allowance for Loan Losses
Total loans	93,239		96,261	98,527
Non-acquired loans | Substandard
Loans and Allowance for Loan Losses
Total loans	41,672		47,430	52,570
Non-acquired loans | Doubtful
Loans and Allowance for Loan Losses
Total loans			22	22
Non-acquired loans | Commercial non-owner occupied real estate
Loans and Allowance for Loan Losses
Total loans	1,192,773		889,756	778,566
Non-acquired loans | Commercial non-owner occupied real estate | Construction and land development
Loans and Allowance for Loan Losses
Total loans	562,336		401,979	372,077
Non-acquired loans | Commercial non-owner occupied real estate | Construction and land development | Pass
Loans and Allowance for Loan Losses
Total loans	548,984		382,167	349,808
Non-acquired loans | Commercial non-owner occupied real estate | Construction and land development | Special mention
Loans and Allowance for Loan Losses
Total loans	8,492		13,633	15,629
Non-acquired loans | Commercial non-owner occupied real estate | Construction and land development | Substandard
Loans and Allowance for Loan Losses
Total loans	4,860		6,179	6,640
Non-acquired loans | Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate
Loans and Allowance for Loan Losses
Total loans	630,437		487,777	406,489
Non-acquired loans | Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate | Pass
Loans and Allowance for Loan Losses
Total loans	615,521		471,466	388,303
Non-acquired loans | Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate | Special mention
Loans and Allowance for Loan Losses
Total loans	11,499		13,912	14,888
Non-acquired loans | Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate | Substandard
Loans and Allowance for Loan Losses
Total loans	3,417		2,399	3,298
Non-acquired loans | Commercial owner occupied real estate loan
Loans and Allowance for Loan Losses
Total loans	1,153,480		1,033,398	1,012,428
Non-acquired loans | Commercial owner occupied real estate loan | Pass
Loans and Allowance for Loan Losses
Total loans	1,118,421		994,442	970,090
Non-acquired loans | Commercial owner occupied real estate loan | Special mention
Loans and Allowance for Loan Losses
Total loans	26,429		29,478	28,799
Non-acquired loans | Commercial owner occupied real estate loan | Substandard
Loans and Allowance for Loan Losses
Total loans	8,630		9,478	13,539
Non-acquired loans | Consumer real estate
Loans and Allowance for Loan Losses
Total loans	1,547,266		1,338,239	1,296,426
Non-acquired loans | Consumer real estate | Home equity loans
Loans and Allowance for Loan Losses
Total loans	363,825		319,255	308,563
Non-acquired loans | Consumer real estate | Home equity loans | Pass
Loans and Allowance for Loan Losses
Total loans	349,382		304,744	294,712
Non-acquired loans | Consumer real estate | Home equity loans | Special mention
Loans and Allowance for Loan Losses
Total loans	8,493		8,171	7,987
Non-acquired loans | Consumer real estate | Home equity loans | Substandard
Loans and Allowance for Loan Losses
Total loans	5,950		6,318	5,842
Non-acquired loans | Consumer real estate | Home equity loans | Doubtful
Loans and Allowance for Loan Losses
Total loans			22	22
Non-acquired loans | Consumer real estate | Consumer
Loans and Allowance for Loan Losses
Total loans	1,864,740		1,617,916	1,571,137
Non-acquired loans | Consumer real estate | Consumer | Pass
Loans and Allowance for Loan Losses
Total loans	1,820,767		1,567,391	1,521,251
Non-acquired loans | Consumer real estate | Consumer | Special mention
Loans and Allowance for Loan Losses
Total loans	23,474		26,719	26,082
Non-acquired loans | Consumer real estate | Consumer | Substandard
Loans and Allowance for Loan Losses
Total loans	20,499		23,784	23,782
Non-acquired loans | Consumer real estate | Consumer | Doubtful
Loans and Allowance for Loan Losses
Total loans			22	22
Non-acquired loans | Consumer real estate | Consumer Owner Occupied Loans
Loans and Allowance for Loan Losses
Total loans	1,183,441		1,018,984	987,863
Non-acquired loans | Consumer real estate | Consumer Owner Occupied Loans | Pass
Loans and Allowance for Loan Losses
Total loans	1,155,481		984,780	953,523
Non-acquired loans | Consumer real estate | Consumer Owner Occupied Loans | Special mention
Loans and Allowance for Loan Losses
Total loans	14,370		17,777	17,198
Non-acquired loans | Consumer real estate | Consumer Owner Occupied Loans | Substandard
Loans and Allowance for Loan Losses
Total loans	13,590		16,427	17,142
Non-acquired loans | Commercial and industrial
Loans and Allowance for Loan Losses
Total loans	617,525		503,808	462,588
Non-acquired loans | Commercial and industrial | Pass
Loans and Allowance for Loan Losses
Total loans	604,058		497,572	456,912
Non-acquired loans | Commercial and industrial | Special mention
Loans and Allowance for Loan Losses
Total loans	11,246		4,472	4,321
Non-acquired loans | Commercial and industrial | Substandard
Loans and Allowance for Loan Losses
Total loans	2,221		1,764	1,355
Non-acquired loans | Other income producing property
Loans and Allowance for Loan Losses
Total loans	179,595		175,848	169,997
Non-acquired loans | Other income producing property | Pass
Loans and Allowance for Loan Losses
Total loans	165,451		163,975	157,233
Non-acquired loans | Other income producing property | Special mention
Loans and Allowance for Loan Losses
Total loans	12,099		8,047	8,808
Non-acquired loans | Other income producing property | Substandard
Loans and Allowance for Loan Losses
Total loans	2,045		3,826	3,956
Non-acquired loans | Consumer
Loans and Allowance for Loan Losses
Total loans	305,687		233,104	223,210
Non-acquired loans | Consumer | Pass
Loans and Allowance for Loan Losses
Total loans	304,117		231,294	221,515
Non-acquired loans | Consumer | Special mention
Loans and Allowance for Loan Losses
Total loans	611		771	897
Non-acquired loans | Consumer | Substandard
Loans and Allowance for Loan Losses
Total loans	959		1,039	798
Non-acquired loans | Commercial
Loans and Allowance for Loan Losses
Total loans	3,143,373		2,602,810	2,423,579
Non-acquired loans | Commercial | Pass
Loans and Allowance for Loan Losses
Total loans	3,052,435		2,509,622	2,322,346
Non-acquired loans | Commercial | Special mention
Loans and Allowance for Loan Losses
Total loans	69,765		69,542	72,445
Non-acquired loans | Commercial | Substandard
Loans and Allowance for Loan Losses
Total loans	21,173		23,646	28,788
Non-acquired loans | Other loans
Loans and Allowance for Loan Losses
Total loans	11,787		46,573	51,501
Non-acquired loans | Other loans | Pass
Loans and Allowance for Loan Losses
Total loans	11,787		$ 46,573	51,501
Acquired credit impaired loans
Loans and Allowance for Loan Losses
Total loans	636,020			773,080
Acquired credit impaired loans | Residential real estate
Loans and Allowance for Loan Losses
Total loans	268,968			330,754
Acquired credit impaired loans | Commercial non-owner occupied real estate | Construction and land development
Loans and Allowance for Loan Losses
Total loans	47,081			55,168
Acquired credit impaired loans | Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate
Loans and Allowance for Loan Losses
Total loans	220,489			266,465
Acquired credit impaired loans | Consumer real estate
Loans and Allowance for Loan Losses
Total loans	61,866			73,632
Acquired credit impaired loans | Commercial and industrial
Loans and Allowance for Loan Losses
Total loans	26,658			34,074
Acquired credit impaired loans | Single pay loans
Loans and Allowance for Loan Losses
Total loans				24
Acquired credit impaired loans | Commercial loans 1000000 or more
Loans and Allowance for Loan Losses
Total loans	10,958			12,963
Acquired non-credit impaired loans
Loans and Allowance for Loan Losses
Total loans	885,657			1,107,440
Acquired non-credit impaired loans | Commercial non-owner occupied real estate | Construction and land development
Loans and Allowance for Loan Losses
Total loans	10,683			16,482
Acquired non-credit impaired loans | Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate
Loans and Allowance for Loan Losses
Total loans	35,775			42,172
Acquired non-credit impaired loans | Commercial owner occupied real estate loan
Loans and Allowance for Loan Losses
Total loans	29,444			42,524
Acquired non-credit impaired loans | Consumer real estate | Home equity loans
Loans and Allowance for Loan Losses
Total loans	168,758			203,025
Acquired non-credit impaired loans | Consumer real estate | Consumer Owner Occupied Loans
Loans and Allowance for Loan Losses
Total loans	435,132			542,278
Acquired non-credit impaired loans | Commercial and industrial
Loans and Allowance for Loan Losses
Total loans	14,201			27,459
Acquired non-credit impaired loans | Other income producing property
Loans and Allowance for Loan Losses
Total loans	43,152			56,092
Acquired non-credit impaired loans | Consumer
Loans and Allowance for Loan Losses
Total loans	$ 148,512			$ 177,408