Schedule II - Valuation and Qualifying Accounts (Details) - Deferred tax valuation allowances - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation allowances and reserves [Roll Forward]
Balance at Beginning of Period	$ 12,881	$ 10,433	$ 7,615
Charged to Costs and Expenses	699	2,426	2,315
Charged to Other Accounts	(1)	22	503
Deductions	0	0	0
Balance at End of Period	$ 13,579	$ 12,881	$ 10,433