Fair Value Measurements Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified						3 Months Ended
	Mar. 31, 2013 Swap [Member] Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure		Dec. 30, 2012 Swap [Member] Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure		Sep. 30, 2008 6.20% senior notes	Mar. 31, 2013 6.20% senior notes Interest Rate Swap [Member]	Apr. 01, 2012 6.20% senior notes Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					6.20%
Notional amount of interest rate swaps						$ 225,000
Interest Rate Derivative Assets, at Fair Value	6,791	[1]	8,169	[1]
Interest income on interest rate swaps						$ 1,435	$ 1,326

[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.