Schedule II, Valuation and Qualifying Accounts (Details) (Allowance for Bad Debts, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Allowance for Bad Debts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1	$ 22,505		$ 21,918		$ 24,698
Charged to costs and expenses	17,005		16,784		16,323
Charged to other accounts	6,240	[1]	7,005	[1]	7,648	[1]
Deductions from reserves	22,628	[2]	23,202	[2]	26,751	[2]
Balance at Dec. 31	$ 23,122		$ 22,505		$ 21,918

[1] Recovery of amounts previously written off.

[2] Principally bad debts written off.