Schedule II, Valuation and Qualifying Accounts (Details) - Allowance for Bad Debts - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1		$ 5,839	$ 5,475	$ 4,722
Charged to costs and expenses		4,655	4,137	3,437
Charged to other accounts	[1]	1,036	1,089	1,076
Deductions from reserves	[2]	5,642	4,862	3,760
Balance at Dec. 31		$ 5,888	$ 5,839	$ 5,475

[1] Recovery of amounts previously written off.

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