Loans and Allowance for Loan Losses - Disaggregated analysis of activity in the allowance for acquired credit impaired loans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for loan losses:
Provision for loan losses before benefit attributable to FDIC loss share agreements	$ 6,796,000	$ 5,078,000	$ 4,170,000
Benefits attributable to FDIC loss share agreements	23,000	786,000	2,420,000
Total provision for loan losses charged to operations	6,819,000	5,864,000	6,590,000
Provision for loan losses recorded through the FDIC loss share receivable	23,000	786,000	2,420,000
Reduction due to loan removals	(899,000)	(3,407,000)	(2,346,000)
Balance at the end of the period	0
Non-acquired loans
Allowance for loan losses:
Provision for loan losses before benefit attributable to FDIC loss share agreements	5,539,000	2,930,000	5,150,000
Total provision for loan losses charged to operations	5,539,000	2,930,000	5,150,000
Loans individually evaluated for impairment	1,337,000	1,607,000	1,558,000
Loans collectively evaluated for impairment	35,623,000	32,483,000	32,981,000
Loans:
Loans individually evaluated for impairment	21,211,000	30,218,000	27,085,000
Loans collectively evaluated for impairment	5,219,830,000	4,190,508,000	3,440,741,000
Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	3,706,000	7,365,000	11,618,000
Provision for loan losses before benefit attributable to FDIC loss share agreements	588,000	(252,000)	(1,907,000)
Benefits attributable to FDIC loss share agreements	23,000	786,000	2,420,000
Total provision for loan losses charged to operations	611,000	534,000	513,000
Provision for loan losses recorded through the FDIC loss share receivable	23,000	786,000	2,420,000
Reduction due to loan removals	(899,000)	(3,407,000)	(2,346,000)
Balance at the end of the period	3,395,000	3,706,000	7,365,000
Loans collectively evaluated for impairment	3,395,000	3,706,000	7,365,000
Loans:
Loans collectively evaluated for impairment	605,941,000	737,576,000	926,767,000
Total acquired loans	605,941,000	737,576,000	926,767,000
Residential real estate
Loans:
Total acquired loans	258,100,000	313,319,000
Residential real estate | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	2,986,000	4,387,000	5,132,000
Provision for loan losses before benefit attributable to FDIC loss share agreements	(129,000)	99,000	(406,000)
Benefits attributable to FDIC loss share agreements	23,000	228,000	571,000
Total provision for loan losses charged to operations	(106,000)	327,000	165,000
Provision for loan losses recorded through the FDIC loss share receivable	23,000	228,000	571,000
Reduction due to loan removals	(438,000)	(1,500,000)	(339,000)
Balance at the end of the period	2,419,000	2,986,000	4,387,000
Loans collectively evaluated for impairment	2,419,000	2,986,000	4,387,000
Loans:
Loans collectively evaluated for impairment	258,100,000	313,319,000	390,244,000
Total acquired loans	258,100,000	313,319,000	390,244,000
Commercial non-owner occupied real estate | Construction and land development | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	(778,000)	(1,707,000)	(1,307,000)
Loans individually evaluated for impairment	348,000	615,000	475,000
Loans collectively evaluated for impairment	3,743,000	3,501,000	5,191,000
Loans:
Loans individually evaluated for impairment	3,033,000	6,280,000	4,852,000
Loans collectively evaluated for impairment	577,431,000	395,699,000	359,369,000
Commercial non-owner occupied real estate | Construction and land development | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	177,000	336,000	2,244,000
Provision for loan losses before benefit attributable to FDIC loss share agreements		(68,000)	(621,000)
Benefits attributable to FDIC loss share agreements		74,000	792,000
Total provision for loan losses charged to operations		6,000	171,000
Provision for loan losses recorded through the FDIC loss share receivable		74,000	792,000
Reduction due to loan removals	(38,000)	(91,000)	(1,287,000)
Balance at the end of the period	139,000	177,000	336,000
Loans collectively evaluated for impairment	139,000	177,000	336,000
Loans:
Loans collectively evaluated for impairment	44,373,000	54,272,000	65,262,000
Total acquired loans	44,373,000	54,272,000	65,262,000
Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	1,011,000	503,000	(471,000)
Loans individually evaluated for impairment	170,000	34,000	77,000
Loans collectively evaluated for impairment	4,810,000	3,534,000	3,077,000
Loans:
Loans individually evaluated for impairment	806,000	1,452,000	3,610,000
Loans collectively evaluated for impairment	713,909,000	486,325,000	329,980,000
Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	56,000	1,444,000	1,816,000
Provision for loan losses before benefit attributable to FDIC loss share agreements	1,000	(456,000)	(328,000)
Benefits attributable to FDIC loss share agreements		459,000	364,000
Total provision for loan losses charged to operations	1,000	3,000	36,000
Provision for loan losses recorded through the FDIC loss share receivable		459,000	364,000
Reduction due to loan removals	(16,000)	(932,000)	(44,000)
Balance at the end of the period	41,000	56,000	1,444,000
Loans collectively evaluated for impairment	41,000	56,000	1,444,000
Loans:
Loans collectively evaluated for impairment	210,204,000	255,430,000	325,109,000
Total acquired loans	210,204,000	255,430,000	325,109,000
Consumer real estate | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	313,000	275,000	538,000
Provision for loan losses before benefit attributable to FDIC loss share agreements	533,000	336,000	(111,000)
Benefits attributable to FDIC loss share agreements		(107,000)	141,000
Total provision for loan losses charged to operations	533,000	229,000	30,000
Provision for loan losses recorded through the FDIC loss share receivable		(107,000)	141,000
Reduction due to loan removals	(288,000)	(298,000)	(152,000)
Balance at the end of the period	558,000	313,000	275,000
Loans collectively evaluated for impairment	558,000	313,000	275,000
Loans:
Loans collectively evaluated for impairment	59,300,000	70,734,000	85,449,000
Total acquired loans	59,300,000	70,734,000	85,449,000
Consumer real estate | Home equity loans | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	791,000	403,000	978,000
Loans individually evaluated for impairment	40,000	3,000	1,000
Loans collectively evaluated for impairment	3,171,000	2,926,000	2,828,000
Loans:
Loans individually evaluated for impairment	1,674,000	309,000	31,000
Loans collectively evaluated for impairment	381,544,000	318,946,000	283,903,000
Commercial and industrial
Loans:
Total acquired loans	25,347,000	31,193,000
Commercial and industrial | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	1,452,000	(74,000)	819,000
Loans individually evaluated for impairment	386,000	279,000	41,000
Loans collectively evaluated for impairment	4,456,000	3,695,000	3,520,000
Loans:
Loans individually evaluated for impairment	1,263,000	1,487,000	908,000
Loans collectively evaluated for impairment	670,135,000	502,321,000	405,015,000
Commercial and industrial | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	174,000	718,000	1,481,000
Provision for loan losses before benefit attributable to FDIC loss share agreements	183,000	(118,000)	(314,000)
Benefits attributable to FDIC loss share agreements		131,000	371,000
Total provision for loan losses charged to operations	183,000	13,000	57,000
Provision for loan losses recorded through the FDIC loss share receivable		131,000	371,000
Reduction due to loan removals	(119,000)	(426,000)	(449,000)
Balance at the end of the period	238,000	174,000	718,000
Loans collectively evaluated for impairment	238,000	174,000	718,000
Loans:
Loans collectively evaluated for impairment	25,347,000	31,193,000	44,804,000
Total acquired loans	25,347,000	31,193,000	44,804,000
Other income producing property | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	(501,000)	(252,000)	(159,000)
Loans individually evaluated for impairment	242,000	422,000	646,000
Loans collectively evaluated for impairment	1,300,000	1,541,000	1,586,000
Loans:
Loans individually evaluated for impairment	2,372,000	4,891,000	5,498,000
Loans collectively evaluated for impairment	175,866,000	170,957,000	145,430,000
Consumer
Loans:
Total acquired loans	59,300,000	70,734,000
Consumer | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	3,310,000	2,890,000	3,058,000
Loans individually evaluated for impairment	4,000	3,000	2,000
Loans collectively evaluated for impairment	2,346,000	1,691,000	1,365,000
Loans:
Loans individually evaluated for impairment	145,000	102,000	60,000
Loans collectively evaluated for impairment	324,093,000	233,002,000	189,257,000
Consumer | Acquired credit impaired loans
Loans:
Total acquired loans	59,300,000	70,734,000
Commercial loans 1000000 or more | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period		135,000	303,000
Provision for loan losses before benefit attributable to FDIC loss share agreements		(43,000)	(129,000)
Benefits attributable to FDIC loss share agreements			183,000
Total provision for loan losses charged to operations		(43,000)	54,000
Provision for loan losses recorded through the FDIC loss share receivable			183,000
Reduction due to loan removals		(92,000)	(39,000)
Balance at the end of the period			135,000
Loans collectively evaluated for impairment			135,000
Loans:
Loans collectively evaluated for impairment	8,617,000	12,628,000	15,813,000
Total acquired loans	$ 8,617,000	12,628,000	15,813,000
Single pay loans | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period		70,000	104,000
Provision for loan losses before benefit attributable to FDIC loss share agreements		(2,000)	2,000
Benefits attributable to FDIC loss share agreements		1,000	(2,000)
Total provision for loan losses charged to operations		(1,000)
Provision for loan losses recorded through the FDIC loss share receivable		1,000	(2,000)
Reduction due to loan removals		$ (68,000)	(36,000)
Balance at the end of the period			70,000
Loans collectively evaluated for impairment			70,000
Loans:
Loans collectively evaluated for impairment			86,000
Total acquired loans			$ 86,000