Schedule II - Valuation And Qualifying Accounts And Reserves Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 3,773	$ 5,199	$ 5,039
Additions charged to costs and expenses	348	785	1,191
Deductions and net write-offs	(1,671)	(2,211)	(1,031)
Balance at end of period	$ 2,450	$ 3,773	$ 5,199