Long-Term Debt (Convertible Senior Notes Dues 2032) (Details) (USD $)	6 Months Ended		1 Months Ended	6 Months Ended
	Jun. 30, 2014		Mar. 31, 2012 Convertible Senior Notes 2032 [Member]	Jun. 30, 2014 Convertible Senior Notes 2032 [Member]		Jun. 30, 2013 Convertible Senior Notes 2032 [Member]	Mar. 31, 2012 Convertible Senior Notes 2025 [Member]	Mar. 31, 2005 Convertible Senior Notes 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 582,513,000		$ 200,000,000	$ 200,000,000	[1]
Debt instrument interest rate			3.25%					3.25%
Proceeds from issuance of debt			195,000,000
Debt instrument, repurchase amount							142,200,000
Convertible Senior Notes, shares of common stock				39.9752
Base principal amount				1,000
Per share conversion price				$ 25.02		$ 25.02
Debt instrument, redemption price, percentage of principal amount redeemed				100.00%
Unamortized debt discount	$ 23,751,000	[2]	$ 35,400,000	$ 23,751,000	[1],[2]
Expected life used to estimate fair value	6 years
Effective interest rate				6.90%

[1] Beginning in March 2018, the holders of the Convertible Senior Notes due 2032 may require us to repurchase these notes or we may at our option elect to repurchase these notes. The notes will mature in March 2032.

[2] The Convertible Senior Notes due 2032 will increase to their principal amount through accretion of non-cash interest charges through March 2018.