Schedule II, Valuation and Qualifying Accounts (Details) (Allowance for Bad Debts, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Allowance for Bad Debts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1	$ 4,722		$ 5,380		$ 5,095
Charged to costs and expenses	3,437		2,915		3,655
Charged to other accounts	1,076	[1]	1,202	[1]	1,139	[1]
Deductions from reserves	3,760	[2]	4,775	[2]	4,509	[2]
Balance at Dec. 31	$ 5,475		$ 4,722		$ 5,380

[1] Recovery of amounts previously written off.

[2] Principally bad debts written off.