Convertible Notes (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended	6 Months Ended
	Feb. 28, 2011	Jun. 30, 2011	Jun. 30, 2011
Convertible Notes
Issuance date	February 2011
2018 Convertible notes, maturity date			Feb. 01, 2018
Cash proceeds from the sale of the notes			$ 222,700,000
Principal amount of notes purchased by underwriters to cover over- allotments			30,000,000
Notes bear cash interest		4.75%	4.75%
Date of commencement of repayment of notes			August 1, 2011
Number of shares of common stock issued upon conversion of notes			86.6739
Principal amount of notes for which number of shares of common stock issued upon conversion		1,000	1,000
Conversion price per share		$ 11.54	$ 11.54
Percentage of redemption price to principal amount of notes			100.00%
Interest expense on convertible notes		4,876,000	7,987,000
Non-cash interest expense		2,200,000	2,200,000
Accrued interest		2,700,000	4,400,000
Accretion of discount on convertible notes			3,587,000
Amortization of deferred financing costs		$ 193,000	$ 320,000