Income Taxes - Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 8,579	$ 10,474
Additions based on tax positions related to the current year	866	981
Additions for tax positions of prior years	1,292	2,549
Reductions for tax positions of prior years - Settlement	(1,689)	(5,425)
Reduction for tax positions of prior years - Statute of limitations	(1,631)	0
Balance at end of year	$ 7,417	$ 8,579