Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS - TDR Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Troubled Debt Restructuring Activity Rollforward [Roll Forward]
Beginning balance	$ 26,329
Ending balance	22,244	$ 5,224
Material commitments to lend additional funds to borrowers with TDRs	0		$ 0
Accruing
Troubled Debt Restructuring Activity Rollforward [Roll Forward]
Beginning balance	1,796	2,291
Additions	0	922
Net payments	(18)	(24)
Net transfers from (to) non-accrual	0	(1,077)
Ending balance	1,778	2,112
Non-accrual
Troubled Debt Restructuring Activity Rollforward [Roll Forward]
Beginning balance	24,533	6,297
Additions	355	0
Net payments	(3,113)	(4,150)
Charge-offs	(1,309)	(112)
Net transfers from accruing	0	1,077
Ending balance	$ 20,466	$ 3,112