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		$ 20,122	$ 23,122	$ 22,505
Charged to costs and expenses		14,121	13,052	17,005
Charged to other accounts	[1]	4,447	5,175	6,240
Deductions from reserves	[2]	19,078	21,227	22,628
Balance at Dec. 31		$ 19,612	$ 20,122	$ 23,122

[1] Recovery of amounts previously written off.

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