Accumulated Comprehensive Loss Total Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Aug. 31, 2010 Interest Rate Swap [Member]	Jul. 31, 2010 Interest Rate Swap [Member]
Debt Instrument, Face Amount					$ 250,000,000
Debt Instrument, Fixed Rate Debt, Term Of Debt					10 years
Settlement of forward starting interest rate swap agreement	0	0	(8,663,000)	(8,700,000)
Interest expense	$ 27,189,000	$ 12,939,000	$ 6,680,000	$ 100,000