Total Debt (Details) (USD $)	12 Months Ended					0 Months Ended	12 Months Ended			12 Months Ended					12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Revolving Credit Facility [Member]	Dec. 31, 2011 Revolving Credit Facility [Member]	Nov. 02, 2010 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2011 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Oct. 31, 2010 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member] Debt Covenant, Net Worth, Sum [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member] Minimum	Dec. 31, 2012 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member] Maximum	Dec. 31, 2012 Line of Credit [Member]	Dec. 31, 2011 Line of Credit [Member]	Dec. 31, 2011 Convertible Notes Payable [Member]	Dec. 31, 2010 Convertible Notes Payable [Member]	Dec. 31, 2004 Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Total long-term debt	$ 0	$ 127,563,000		$ 0	$ 125,000,000								$ 0	$ 2,563,000
Current maturities of long-term debt	209,728,000	0		205,000,000	0								4,728,000	0
Total debt	209,728,000	127,563,000
Debt instrument, face amount							375,000,000		275,000,000								16,700,000
Loan origination fees	(67,000)	(155,000)	(421,000)			500,000
Amendment, decrease in pricing schedule									0.375%
Amendment, decrease in commitment fee									0.05%
Variable rate basis							LIBOR
Margin on variable rate											1.625%	3.125%
Commitment fee, unused capacity											0.25%	0.45%
Effective interest rate during period							1.87%	2.19%
Debt covenant, interest coverage ratio											3.5
Debt covenant, leverage ratio											3.25
Debt covenant, minimum net worth, base										350,000,000
Debt covenant, minimum net worth, percent of net income										50.00%
Debt covenant, minimum net worth, percent of net proceeds from future debt or equity offerings										100.00%
Remaining borrowing capacity							159,000,000
Shares acquired																	452,603
Issuance of common stock for convertible note payable, shares															452,603
Gain on conversion of debt															2,700,000
Interest Expense	4,531,000	8,924,000	6,179,000												1,400,000
Gain on long put option and short call option																$ 800,000