Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 2,911	$ 4,454	$ 5,837
Additions Charged to Costs and Expenses	1,923	2,069	1,184
Deductions	2,293	3,612	2,567
Balance at End of Period	2,541	2,911	4,454
Deferred tax valuation allowance
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	191,922	193,405	165,020
Additions Charged to Costs and Expenses	14,232	7,599	28,418
Deductions	78,227	9,082	33
Balance at End of Period	$ 127,927	$ 191,922	$ 193,405