Fair Value Measurements Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified				3 Months Ended		9 Months Ended
	Sep. 30, 2012	Jan. 01, 2012	Sep. 30, 2012 6.20% senior notes	Sep. 30, 2012 6.20% senior notes Interest Rate Swap [Member]	Oct. 02, 2011 6.20% senior notes Interest Rate Swap [Member]	Sep. 30, 2012 6.20% senior notes Interest Rate Swap [Member]	Oct. 02, 2011 6.20% senior notes Interest Rate Swap [Member]	May 15, 2012 Senior Notes	Sep. 30, 2012 Swap [Member] Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]		Jan. 01, 2012 Swap [Member] Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]		Sep. 30, 2012 Swap [Member] Fair Value, Inputs, Level 2 [Member] Carrying (Reported) Amount, Fair Value Disclosure [Member]		Jan. 01, 2012 Swap [Member] Fair Value, Inputs, Level 2 [Member] Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivatives, Fair Value [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.20%					10.00%
Notional amount of interest rate swaps				$ 225,000		$ 225,000
Interest Rate Derivative Assets, at Fair Value									9,618	[1]	11,695	[1]	9,618	[1]	11,695	[1]
Interest income on interest rate swaps				1,283	1,402	4,013	4,250
Long-term debt	$ 1,457,328	$ 1,356,999

[1] The fair values were based on information provided by the bank counterparties that is model-driven and where inputs were observable or where significant value drivers were observable.