Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for loan losses:
Beginning balance				$ 75,032				$ 66,037	$ 75,032	$ 66,037	$ 62,453
Provision for losses	$ 1,664	$ 1,400	$ 1,663	2,500	$ 1,800	$ 2,083	$ 2,875	2,385	7,227	9,143	5,657
Recoveries on loans									6,276	4,880	5,356
Loans charged off									(7,983)	(5,028)	(7,429)
Ending balance	80,552				75,032				80,552	75,032	66,037
Commercial
Allowance for loan losses:
Beginning balance				30,418				27,696	30,418	27,696	26,478
Provision for losses									2,097	2,515	1,876
Recoveries on loans									2,456	1,590	1,806
Loans charged off									(2,316)	(1,383)	(2,464)
Ending balance	32,655				30,418				32,655	30,418	27,696
Commercial Real Estate
Allowance for loan losses:
Beginning balance				27,343				23,661	27,343	23,661	22,145
Provision for losses									2,482	3,159	1,834
Recoveries on loans									2,525	2,260	2,090
Loans charged off									(2,741)	(1,737)	(2,408)
Ending balance	29,609				27,343				29,609	27,343	23,661
Consumer
Allowance for loan losses:
Beginning balance				3,732				2,923	3,732	2,923	2,689
Provision for losses									679	1,078	432
Recoveries on loans									302	324	369
Loans charged off									(749)	(593)	(567)
Ending balance	3,964				3,732				3,964	3,732	2,923
Residential
Allowance for loan losses:
Beginning balance				13,537				11,755	13,537	11,755	11,139
Provision for losses									1,969	2,391	1,515
Recoveries on loans									993	706	1,091
Loans charged off									(2,177)	(1,315)	(1,990)
Ending balance	14,322				13,537				14,322	13,537	11,755
Finance Leases
Allowance for loan losses:
Beginning balance				$ 2				$ 2	2	2	2
Provision for losses
Recoveries on loans
Loans charged off
Ending balance	$ 2				$ 2				$ 2	$ 2	$ 2