Schedule II - Valuation and Qualifying Accounts - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance at Beginning of Period	$ 87,626
Balance at End of Period	66,437	$ 87,626
Valuation Allowance of Deferred Tax Assets [Member]
Balance at Beginning of Period	87,626	80,505	$ 71,939
Additions Charged to Costs and Expenses	9,486	7,121	8,566
Additions Charged to Other Accounts
Deductions	(30,675)
Balance at End of Period	$ 66,437	$ 87,626	$ 80,505