Convertible Notes (Narrative) (Details) (USD $)	1 Months Ended	12 Months Ended
	Feb. 28, 2011	Dec. 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 Convertible 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 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		15,737,000
Non-cash interest expense		5,700,000
Accrued interest		$ 10,000,000