Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 331	$ 368
Gross increases – tax positions in current period	22	2
Lapse of statute of limitations	(25)	(39)
Ending balance	$ 328	$ 331