Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits and Related Accrued Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Tax Benefits
Beginning balance	$ 193	$ 497	$ 535
Additions based on tax positions related to the current year	4	0	0
Additions based on tax positions related to the prior years	10	116	0
Decrease based on payments made during the year	0	0	0
Decreases based on tax positions related to the prior years	0	(420)	(38)
Ending balance	207	193	497
Accrued Interest and Penalties
Beginning balance	28	154	202
Additions based on tax positions related to the current year	0	0	0
Additions based on tax positions related to the prior years	6	19	11
Decrease based on payments made during the year	0	0	0
Decreases based on tax positions related to the prior years	0	(145)	(59)
Ending balance	$ 34	$ 28	$ 154