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	$ 29,938	$ 35,584	$ 23,518
Reductions based on tax positions related to prior year	(820)	(6,335)	(2,100)
Additions based on tax positions related to prior year	263	108	2,809
Additions based on tax positions related to current year	11,860	9,289	11,357
Reductions due to tax authorities’ settlements	(43)	(8,603)	0
Reductions due to expiration of statutes of limitation	0	(105)	0
Balance at end of year	$ 41,198	$ 29,938	$ 35,584