Loans and Allowance for Loan Losses - Allowance for Credit Losses (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance		$ 75,670,000	$ 61,944,000	$ 67,240,000	$ 58,980,000
Charged-off loans		(6,949,000)	(5,987,000)	(22,316,000)	(16,308,000)
Recovery of previously charged-off loans		2,539,000	2,282,000	10,003,000	5,103,000
Provision for loan losses		8,725,000	6,920,000	25,058,000	17,384,000
Ending Balance		79,985,000	65,159,000	79,985,000	65,159,000
Loans acquired with deteriorated credit quality (1)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	[1]			573,000
Ending Balance	[1]	11,000		11,000
Commercial real estate - mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance		24,848,000	16,002,000	21,188,000	13,655,000
Charged-off loans		(1,968,000)	(572,000)	(2,930,000)	(581,000)
Recovery of previously charged-off loans		63,000	169,000	1,517,000	184,000
Provision for loan losses		3,574,000	5,191,000	6,742,000	7,532,000
Ending Balance		26,517,000	20,790,000	26,517,000	20,790,000
Commercial real estate - mortgage | Loans acquired with deteriorated credit quality (1)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	[1]			340,000
Ending Balance	[1]	9,000		9,000
Consumer real estate - mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance		5,853,000	7,835,000	5,031,000	6,564,000
Charged-off loans		(262,000)	(395,000)	(1,533,000)	(663,000)
Recovery of previously charged-off loans		987,000	565,000	2,190,000	1,147,000
Provision for loan losses		149,000	(2,702,000)	1,039,000	(1,745,000)
Ending Balance		6,727,000	5,303,000	6,727,000	5,303,000
Consumer real estate - mortgage | Loans acquired with deteriorated credit quality (1)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	[1]			161,000
Ending Balance	[1]	2,000		2,000
Construction and land development
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance		10,984,000	5,126,000	8,962,000	3,624,000
Charged-off loans		(24,000)	(99,000)	(36,000)	(99,000)
Recovery of previously charged-off loans		70,000	716,000	1,645,000	845,000
Provision for loan losses		(48,000)	1,780,000	411,000	3,153,000
Ending Balance		10,982,000	7,523,000	10,982,000	7,523,000
Construction and land development | Loans acquired with deteriorated credit quality (1)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	[1]			17,000
Ending Balance	[1]	0		0
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance		28,338,000	24,235,000	24,863,000	24,743,000
Charged-off loans		(3,336,000)	(1,625,000)	(7,600,000)	(3,278,000)
Recovery of previously charged-off loans		1,037,000	562,000	2,492,000	1,264,000
Provision for loan losses		4,085,000	235,000	10,369,000	678,000
Ending Balance		30,124,000	23,407,000	30,124,000	23,407,000
Commercial and industrial | Loans acquired with deteriorated credit quality (1)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	[1]			55,000
Ending Balance	[1]	0		0
Consumer and other
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance		5,172,000	7,549,000	5,874,000	9,520,000
Charged-off loans		(1,359,000)	(3,296,000)	(10,217,000)	(11,687,000)
Recovery of previously charged-off loans		382,000	270,000	2,159,000	1,663,000
Provision for loan losses		618,000	2,396,000	6,997,000	7,423,000
Ending Balance		4,813,000	6,919,000	4,813,000	6,919,000
Consumer and other | Loans acquired with deteriorated credit quality (1)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	[1]			0
Ending Balance	[1]	0		0
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance		475,000	1,197,000	1,322,000	874,000
Charged-off loans		0	0	0	0
Recovery of previously charged-off loans		0	0	0	0
Provision for loan losses		347,000	20,000	(500,000)	343,000
Ending Balance		822,000	$ 1,217,000	822,000	$ 1,217,000
Unallocated | Loans acquired with deteriorated credit quality (1)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	[1]
Ending Balance	[1]

[1] (1) Loans acquired with deteriorated credit quality are recorded at fair value at the time of acquisition. An allowance for loan losses is recorded resulting from subsequent credit deterioration.