Income Taxes - Reconciliation of Beginning and Ending Amounts of 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]
Balance at beginning of year	$ 10,474	$ 7,293
Additions based on tax positions related to the current year	981	507
Additions for tax positions of prior years	2,549	2,675
Reductions for tax positions of prior years - Settlement	(5,425)	0
Reduction for tax positions of prior years - Statute of limitations	0	(1)
Balance at end of year	$ 8,579	$ 10,474