Derivative Financial Instruments (Details) (USD $)	1 Months Ended	6 Months Ended
	Mar. 31, 2011	Jun. 30, 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		1,256,000	1,998,000
Accrued expenses
Derivative financial instrument
Fair value of interest rate swap		1,256,000
Long-term obligations and other liabilities
Derivative financial instrument
Fair value of interest rate swap			$ 1,998,000