Derivative Financial Instruments (Details) (USD $)	1 Months Ended	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2012	Dec. 31, 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		1,696,000	1,998,000
Long-term obligations and other liabilities
Derivative financial instrument
Fair value of interest rate swap			1,998,000
Accrued expenses
Derivative financial instrument
Fair value of interest rate swap		$ 1,696,000