Income Taxes - Rollforward 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
Balance at beginning of year	$ 663	$ 663	$ 663
Additions for tax positions of prior years	16,187	0	0
Balance at end of year	$ 16,850	$ 663	$ 663