Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - TDR Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	$ 8,588	$ 5,067
Additions	33,192	5,122	$ 445
Ending balance	26,329	8,588	5,067
Accruing
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	2,291	2,743	3,704
Additions	15,819	0	120
Net payments	(1,923)	(120)	(774)
Returned to performing status	0	0	0
Net transfers to non-accrual	(14,391)	(332)	(307)
Ending balance	1,796	2,291	2,743
Non-accrual
Troubled Debt Restructuring Activity [Roll Forward]
Beginning balance	6,297	2,324	19,904
Additions	14,570	6,205	325
Net payments	(4,380)	(1,072)	(15,525)
Charge-offs	(6,345)	(1,492)	(2,687)
Transfers to OREO	0	0	0
Loans sold	0	0	0
Net transfers from accruing	14,391	332	307
Ending balance	$ 24,533	$ 6,297	$ 2,324