Income Taxes - Uncertain Tax Positions Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at January 1	$ 665	$ 419	$ 3,786
Additions (reductions) for tax positions of prior years	(399)	477	(95)
Additions (reductions) for tax positions of current year	0
Reductions for settlements with tax authorities		0	(575)
Reductions for lapse of statute of limitations	(9)	(231)	(2,697)
Balance at December 31	$ 257	$ 665	$ 419