Convertible Debt and Credit Facility (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2005	Dec. 31, 2009	Mar. 31, 2012 2005 LOC [Member]	Mar. 31, 2012 2011 LOC [Member]	Jun. 30, 2011 2011 LOC [Member]
Convertible Debt and Credit Facility [Abstract]
Issuance of senior subordinated convertible notes			$ 121,000,000
Stated interest rate (in hundredths)			2.875%
Maturity date			Dec. 15, 2035
Extinguishment of Debt [Line Items]
Convertible Notes repurchased				27,900,000
Long-term debt [Abstract]
Principal amount	93,100,000	93,100,000
Unamortized discount	(2,836,000)	(3,806,000)
Net carrying amount	90,264,000	89,294,000
Current portion of outstanding debt	90,264,000	89,294,000
Noncurrent portion of outstanding debt	0	0
Equity component, net of income tax benefit	16,399,000	16,399,000
Discount rate used on the liability component of long-term debt (in hundredths)	7.50%
Interest expense on Convertible Notes [Abstract]
Contractual interest coupon	665,000	662,000
Non-cash amortization of discount on the liability component	971,000	892,000
Non-cash amortization of debt issuance costs	98,000	92,000
Total	1,734,000	1,646,000
Put options terms	The Notes contain put options, which may require the Company to repurchase in cash all or a portion of the Notes on December 15, 2012, December 15, 2015, December 15, 2020, December 15, 2025, and December 15, 2030 at a repurchase price equal to 100% of the principal amount of the Notes to be repurchased plus accrued and unpaid interest up to but excluding the repurchase date.
Line of Credit Facility [Line Items]
Unsecured line of credit, maximum borrowing capacity					10,000,000	7,000,000	5,000,000
Borrowings outstanding					0	0
Outstanding letters of credit					49,000	5,700,000
Interest rate (in hundredths)					1.20%	1.20%
Basis spread on LIBOR (in hundredths)					1.00%	1.00%
Capitalized interest	$ 198,000	$ 0