Schedule II, Valuation and Qualifying Accounts (Details) - Allowance for Bad Debts - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1		$ 5,128	$ 5,821	$ 4,911
Charged to costs and expenses		3,730	3,947	4,431
Charged to other accounts	[1]	1,008	1,161	1,269
Deductions from reserves	[2]	5,001	5,801	4,790
Balance at Dec. 31		$ 4,865	$ 5,128	$ 5,821

[1] Recovery of amounts previously written off.

[2] Deductions relate primarily to bad debt write-offs.