Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 9,422	$ 8,566	$ 8,152
Additions based on tax positions related to current year	1,087	880	459
Reductions to tax provision of prior years	(529)	(24)	(45)
Balance at end of year	$ 9,980	$ 9,422	$ 8,566