Debt and Capital Lease Obligations (Narrative) (Details)		1 Months Ended			3 Months Ended			6 Months Ended
	Dec. 31, 2015 USD ($)	Oct. 31, 2012 USD ($) $ / shares shares	Jan. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)
Debt Instruments
Credit facility termination fees	$ 200,000
Capitalized Interest
Capitalized interest					$ 2,000,000		$ 1,400,000	$ 3,900,000	$ 2,700,000
1.75% Convertible Debentures [Member]
Debt Instruments
Debt, principal amount		$ 396,750,000
Stated interest rate	1.75%	1.75%			1.75%		1.75%	1.75%	1.75%
Convertible debt ratio		0.0604961
Debt conversion price (in usd per share) | $ / shares		$ 16.53
Embedded conversion feature, warrant, conversion ratio | shares		30.2481
Embedded conversion feature, warrant, conversion price (in usd per share) | $ / shares		$ 16.53
Effective term of debt instrument		7 years
Adjustments to equity, component of convertible debt treated as additional debt discount		$ 141,600,000
Debt issuance costs		$ 12,400,000
Debt and equity issuance costs amortization period		7 years
Principal amount of debt repurchased						$ 61,600,000
Cash paid to repurchase debt						59,400,000
Reduction of debt component						50,700,000
Reduction of debt discount						10,900,000
Write off of debt and equity issuance costs						700,000
Gain (loss) on extinguishment of debt, net						(4,200,000)
Effective interest rate		8.50%
Convertible debentures	$ 254,600,000				$ 263,800,000			$ 263,800,000
Unamortized discount	76,754,000				67,989,000			67,989,000
Deferred debt issue costs	$ 3,821,000				$ 3,384,000			$ 3,384,000
1.875% Convertible Debentures [Member]
Debt Instruments
Stated interest rate	1.875%				1.875%		1.875%	1.875%	1.875%
Principal amount of debt repurchased						1,700,000
Cash paid to repurchase debt						1,600,000
Gain (loss) on extinguishment of debt, net						$ 100,000
Convertible debentures	$ 500,000				$ 500,000			$ 500,000
Credit Agreement [Member]
Debt Instruments
Debt issuance costs			$ 200,000	$ 1,100,000
Credit agreement			$ 125,000,000	$ 100,000,000
Credit Agreement [Member] | Minimum [Member]
Debt Instruments
Commitment fee on unutilized borrowing capacity			0.375%
Credit Agreement [Member] | Maximum [Member]
Debt Instruments
Commitment fee on unutilized borrowing capacity			0.50%