Debt and Capital Lease Obligations (Narrative) (Details)	1 Months Ended					3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 31, 2014 USD ($)	Mar. 31, 2013 USD ($)	Oct. 31, 2012 USD ($) $ / shares shares	Jan. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2000 USD ($)	Dec. 31, 2014 USD ($)
Debt Instruments [Abstract]
Gain (loss) on extinguishment of debt, net						$ (4,010,000)	$ 0	$ (4,010,000)	$ 0
Capital Lease Obligation
Payments on capital lease obligations						500,000	500,000	1,600,000	1,600,000
Capital lease obligations						1,100,000		1,100,000			$ 2,600,000
Capitalized Interest
Capitalized interest						1,500,000	1,400,000	4,200,000	3,600,000
Capital Lease Obligations [Member]
Debt Instruments [Abstract]
Interest paid						100,000	100,000	$ 100,000	100,000
Capital Lease Obligation
Debt instrument term								4 years
Interest paid (less than for capital lease obligations)						$ 100,000	$ 100,000	$ 100,000	$ 100,000
1.75% Convertible Debentures [Member]
Debt Instruments [Abstract]
Debt, principal amount			$ 396,750,000.00
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 and equity issuance costs			$ 12,400,000
Debt and equity issuance costs amortization period			7 years
Net discounted proceeds of the offering			$ 384,300,000
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
Effective interest rate			8.50%
Convertible debentures						254,200,000		$ 254,200,000			$ 291,100,000
Unamortized discount						80,990,000		80,990,000			$ 105,634,000
Interest paid						423,000	$ 0	3,894,000	$ 3,472,000
Capital Lease Obligation
Interest paid (less than for capital lease obligations)						423,000	$ 0	$ 3,894,000	$ 3,472,000
1.75% Convertible Debentures [Member] | Loss on debt extinguishment, net [Member]
Debt Instruments [Abstract]
Gain (loss) on extinguishment of debt, net						$ (4,200,000)
1.875% Convertible Debentures [Member]
Debt Instruments [Abstract]
Stated interest rate		1.875%				1.875%	1.875%	1.875%	1.875%		1.875%
Repayments of convertible debt		$ 164,300,000
Principal amount of debt repurchased						$ 1,700,000
Cash paid to repurchase debt						1,600,000
Convertible debentures						500,000		$ 500,000			$ 500,000
Interest paid						21,000	$ 21,000	42,000	$ 42,000
Capital Lease Obligation
Interest paid (less than for capital lease obligations)						21,000	21,000	42,000	42,000
1.875% Convertible Debentures [Member] | Loss on debt extinguishment, net [Member]
Debt Instruments [Abstract]
Gain (loss) on extinguishment of debt, net						100,000
Credit Agreement [Member]
Debt Instruments [Abstract]
Credit agreement				$ 125,000,000.0	$ 100,000,000.0
Debt issuance costs				$ 200,000	$ 1,100,000
Borrowing base comprised eligible accounts receivable					85.00%
Borrowing base comprised eligible accounts inventories					70.00%
Letter of credit sub-facility					$ 60,000,000.0
Outstanding borrowings						0	0	0	0
Undrawn letters of credit issued as collateral for sureties						$ 17,500,000	$ 17,500,000	$ 17,500,000	$ 17,500,000
Credit Agreement [Member] | Minimum [Member]
Debt Instruments [Abstract]
Basis spread over LIBOR					2.25%
Commitment fee on unutilized borrowing capacity					0.375%
Credit Agreement [Member] | Maximum [Member]
Debt Instruments [Abstract]
Percentage of total borrowing capacity remaining when covenant takes effect (less than)					30.00%
Basis spread over LIBOR					2.75%
Commitment fee on unutilized borrowing capacity					0.50%
8% Series 2000 [Member]
Debt Instruments [Abstract]
Debt, principal amount										$ 30,000,000.0
Stated interest rate										8.00%
Net discounted proceeds of the offering										$ 28,700,000
Effective interest rate										8.57%
Repayment of debt	$ 30,000,000
Interest paid	40,000
Capital Lease Obligation
Interest paid (less than for capital lease obligations)	$ 40,000