Schedule II, Valuation and Qualifying Accounts (Details) (Allowance for Bad Debts [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Allowance for Bad Debts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1	$ 5,380		$ 5,095		$ 4,415
Charged to costs and expenses	2,915		3,655		3,990
Charged to other accounts	1,202	[1]	1,139	[1]	998	[1]
Deductions from reserves	4,775	[2]	4,509	[2]	4,308	[2]
Balance at Dec. 31	$ 4,722		$ 5,380		$ 5,095

[1] Recovery of amounts previously written off.

[2] Principally bad debts written off or transferred.