Income Taxes - Summary of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 0	$ 140	$ 117
Increases in positions taken in a current period	0	0	38
Decreases due to settlements	0	(140)	(15)
Balance at end of period	$ 0	$ 0	$ 140