Convertible Notes (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Convertible Notes [Abstract]
Issuance date	February 2011
Convertible Notes at par	$ 230,000,000
2018 Convertible Notes, maturity date	Feb. 01, 2018
Cash proceeds from the sale of the notes	222,700,000
Interest rate at which Notes bear cash interest	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
Percentage of redemption price to principal amount of Notes	100.00%
Minimum number of trading days for first condition of convertibility of Notes	20
Number of consecutive trading day period during five business day period	5
Number of trading days immediately preceding calendar quarter	30
Minimum percentage of conversion price on each applicable trading day	130.00%
Debt conversion converted instrument, principal amount	1,000
Maximum trading price	98.00%
Interest expense on Convertible Notes	4,384,000	3,111,000
Amortization of deferred financing costs	$ 175,000	$ 128,000