Income Taxes from Continuing Operations - Summary of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits
Balance	$ 1,301	$ 2,285	$ 2,010
Additions relating to current year	416	303	356
Payments of amounts relating to prior years		(1,287)	(81)
Additions relating to prior years	24,297
Terminations of exposures relating to prior years	(619)
Balance	$ 25,395	$ 1,301	$ 2,285