Fair Value of Financial Instruments Nonrecurring Basis (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
Assets measured on nonrecurring basis
Losses on impaired loans charged through allowance for loan losses	$ 1,115	$ 1,086	$ 947	$ 624	$ 711	$ 1,146	$ 727	$ 955
Nonrecurring Basis
Assets measured on nonrecurring basis
Losses on impaired loans charged through allowance for loan losses									$ 0
Nonrecurring Basis | Significant Other Observable Inputs (Level 2)
Assets measured on nonrecurring basis
Impaired loans, aggregate outstanding principal balance	25,700								25,700
Impaired loans, fair value	$ 20,600								$ 20,600