Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowances for Accounts Receivable
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 3,245	$ 4,045	$ 1,425
Charged to Operations	4,705	4,034	2,414
Write-Offs	(4,804)	(5,149)	(923)
Recoveries	542	315	1,129
Other Changes	0	0	0
Balance at End of Period	3,688	3,245	4,045
Valuation Allowance for Deferred Tax Assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	46,454	55,336	63,616
Charged to Operations	(3,007)	(8,894)	(7,518)
Write-Offs	(43,333)	0	0
Recoveries	0	0	0
Other Changes	962	12	(762)
Balance at End of Period	$ 1,076	$ 46,454	$ 55,336