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	$ 4,766		$ 4,262		$ 4,709
Charged to costs and expenses	3,329		3,842		3,294
Charged to other accounts	1,310	[1]	1,241	[1]	1,207	[1]
Deductions from reserves	5,072	[2]	4,579	[2]	4,948	[2]
Balance at Dec. 31	$ 4,333		$ 4,766		$ 4,262

[1] Recovery of amounts previously written off.

[2] Principally bad debts written off or transferred.