Income Taxes - Reconciliation of Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at the beginning of the year	$ 13,330	$ 12,695	$ 0
Additions based on tax positions related to the current year	574	300	12,695
Additions for tax positions from prior years	340	379	0
Subtractions for federal tax reform	(3,296)	0	0
Subtractions for tax positions from prior years	(78)	(44)	0
Unrecognized tax benefits at the end of the year	$ 10,870	$ 13,330	$ 12,695