Income Taxes - Schedule 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]
Gross balance - beginning of year	$ 28,004	$ 27,688
Additions based on tax positions of prior years	145	904
Additions based on tax positions related to the current year	2,903	4,347
Settlements with taxing authorities	0	0
Reductions for tax positions of prior years	(356)	(3,088)
Reductions based on tax positions related to the current year	0	0
Reductions due to lapse of applicable statutes of limitations	(2,275)	(1,847)
Gross balance - end of year	$ 28,421	$ 28,004