Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for loan losses:
Beginning balance				$ 66,037				$ 62,453	$ 66,037	$ 62,453	$ 63,964
Provision for losses	$ 1,800	$ 2,083	$ 2,875	2,385	$ 2,417	$ 1,900	$ 790	550	9,143	5,657	417
Recoveries on loans									4,880	5,356	6,344
Loans charged off									(5,028)	(7,429)	(8,272)
Ending balance	75,032				66,037				75,032	66,037	62,453
Commercial
Allowance for loan losses:
Beginning balance				27,696				26,478	27,696	26,478	28,824
Provision for losses									2,515	1,876	(1,901)
Recoveries on loans									1,590	1,806	1,911
Loans charged off									(1,383)	(2,464)	(2,356)
Ending balance	30,418				27,696				30,418	27,696	26,478
Commercial Real Estate
Allowance for loan losses:
Beginning balance				23,661				22,145	23,661	22,145	19,327
Provision for losses									3,159	1,834	1,710
Recoveries on loans									2,260	2,090	2,545
Loans charged off									(1,737)	(2,408)	(1,437)
Ending balance	27,343				23,661				27,343	23,661	22,145
Consumer
Allowance for loan losses:
Beginning balance				2,923				2,689	2,923	2,689	2,658
Provision for losses									1,078	432	299
Recoveries on loans									324	369	352
Loans charged off									(593)	(567)	(620)
Ending balance	3,732				2,923				3,732	2,923	2,689
Residential
Allowance for loan losses:
Beginning balance				11,755				11,139	11,755	11,139	13,152
Provision for losses									2,391	1,515	310
Recoveries on loans									706	1,091	1,536
Loans charged off									(1,315)	(1,990)	(3,859)
Ending balance	13,537				11,755				13,537	11,755	11,139
Finance Leases
Allowance for loan losses:
Beginning balance				$ 2				$ 2	2	2	3
Provision for losses											(1)
Recoveries on loans
Loans charged off
Ending balance	$ 2				$ 2				$ 2	$ 2	$ 2