Derivative Financial Instruments (Details) (USD $)	1 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2011	Jan. 01, 2011
Derivative Financial Instruments
Description of variable rate		three-month LIBOR
Notional value of interest rate swap agreement hedging headquarters lease through March 2011	$ 44,300,000
Notional value of interest rate swap agreement hedging headquarters lease through March 2013		50,100,000
Derivative financial instrument
Fair value of interest rate swap		1,998,000	3,811,000
Long-term obligations and other liabilities
Derivative financial instrument
Fair value of interest rate swap		1,998,000	3,467,000
Accrued expenses
Derivative financial instrument
Fair value of interest rate swap			$ 344,000