Debt and Capital Lease Obligations (Narrative) (Details) (USD $)	3 Months Ended		1 Months Ended		12 Months Ended	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Oct. 31, 2012	Dec. 31, 2000	Jan. 31, 2012	Dec. 31, 2011	Jul. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Debt Instruments [Abstract]
Amortization expense related to issuance costs (less than in 2015 and 2014 for asset-backed revolving credit agreement)	$ 303,000	$ 364,000
Capital Lease Obligation
Payments on capital lease obligations	500,000	500,000
Capital lease obligations	2,100,000								2,600,000
Capitalized Interest
Capitalized interest	1,300,000	1,100,000
1.875% Convertible Debentures [Member]
Debt Instruments [Abstract]
Stated interest rate	1.875%	1.875%							1.875%
Repayments of convertible debt			164,300,000
Convertible debentures	2,200,000								2,200,000
Amortization expense related to issuance costs (less than in 2015 and 2014 for asset-backed revolving credit agreement)	0	0
Interest expense (less than in 2015 and 2014 for 1.875% debentures)	100,000	100,000
Cash paid for interest (less than in 2015 and 2014 for 1.875% debentures and capital lease obligations)	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%
Convertible debt ratio				0.0604961
Debt conversion price (in usd per share)				$ 16.53
Embedded conversion feature, warrant, conversion ratio				30.2481
Embedded conversion feature, warrant, conversion price (in usd per share)				$ 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
Effective interest rate				8.50%
Convertible debentures	295,600,000								291,100,000
Unamortized discount	101,100,000								105,600,000
Amortization expense related to issuance costs (less than in 2015 and 2014 for asset-backed revolving credit agreement)	200,000	300,000
Interest expense (less than in 2015 and 2014 for 1.875% debentures)	6,300,000	5,900,000
Cash paid for interest (less than in 2015 and 2014 for 1.875% debentures and capital lease obligations)	3,500,000	0
Long-term debt, balance outstanding	396,750,000								396,750,000
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
Unamortized discount										400,000
Effective interest rate					8.57%
Long-term debt, balance outstanding										29,600,000
Credit Agreement [Member]
Debt Instruments [Abstract]
Amortization expense related to issuance costs (less than in 2015 and 2014 for asset-backed revolving credit agreement)	100,000	100,000
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
Asset-backed revolving credit facility fees recognized	300,000	300,000
Outstanding borrowings	0	0
Undrawn letters of credit issued as collateral for sureties	18,100,000	18,100,000
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%
Long-term Debt [Member] | 8% Series 2000 [Member]
Debt Instruments [Abstract]
Cash paid for interest (less than in 2015 and 2014 for 1.875% debentures and capital lease obligations)								40,000
Repayment of debt								30,000,000
Capital Lease Obligations [Member]
Debt Instruments [Abstract]
Cash paid for interest (less than in 2015 and 2014 for 1.875% debentures and capital lease obligations)	$ 100,000	$ 100,000
Capital Lease Obligation
Debt instrument term	4 years