Debt (Details) (USD $) In Thousands	1 Months Ended	6 Months Ended
	Apr. 30, 2011	Jun. 30, 2011	Mar. 31, 2011
Line of credit facility, maximum borrowing capacity			$ 100,000
Possible future increase in credit facility			150,000
Sublimit for letters of credit for working capital requirements and other general corporate purposes			20,000
Principal maturity date		March 7, 2014
Amount available for withdrawal under the revolving credit facility		0
Letters of credit outstanding amount		6,980
Borrowing availability		93,000
Debt instrument, aggregate principal amount	3,000
Additional shares of common stock issued for a conversion of principal amount of 1.375% notes	190,747
Amount of senior notes outstanding		718
1.375% Convertible Senior Notes due February 2012 [Member]
Amount of senior notes outstanding		$ 718