Debt and Capital Lease Obligations (Narrative) (Details) (USD $)	3 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended				1 Months Ended	3 Months Ended						1 Months Ended	3 Months Ended			3 Months Ended
	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2012	Mar. 15, 2013 1.875% Convertible debentures [Member]	Oct. 31, 2009 1.875% Convertible debentures [Member]	Mar. 31, 2013 1.875% Convertible debentures [Member]	Mar. 31, 2012 1.875% Convertible debentures [Member]	Dec. 31, 2012 1.875% Convertible debentures [Member]	Mar. 31, 2008 1.875% Convertible debentures [Member]	Oct. 31, 2012 1.75% Convertible Debentures [Member]	Mar. 31, 2013 1.75% Convertible Debentures [Member]	Dec. 31, 2012 1.75% Convertible Debentures [Member]	Mar. 31, 2012 1.75% Convertible Debentures [Member]	Mar. 31, 2013 8% Series 2000 [Member]	Mar. 31, 2012 8% Series 2000 [Member]	Dec. 31, 2012 8% Series 2000 [Member]	Dec. 31, 2011 Credit Agreement [Member]	Mar. 31, 2013 Credit Agreement [Member]	Mar. 31, 2012 Credit Agreement [Member]	Jan. 13, 2012 Credit Agreement [Member]	Mar. 31, 2013 Credit Agreement [Member] Minimum [Member]	Mar. 31, 2013 Credit Agreement [Member] Maximum [Member]
Debt Instruments [Abstract]
Debt, principal amount									$ 181,500,000	$ 396,750,000.00	$ 396,750,000.00	$ 396,750,000.00		$ 30,000,000.0		$ 30,000,000.0
Debt, maturity date						Mar. 15, 2028								Jul. 01, 2020
Stated interest rate						1.875%		1.875%			1.75%	1.75%		8.00%		8.00%
Convertible debt, frequency of interest payment						semi-annually on March 15 and September 15 of each year
Conversion ratio amount per share						$ 1,000
Common stock issuable on conversion of debt per $1,000 (in shares)						42.5351					60.4961
Debt conversion price (in usd per share)						$ 23.51					$ 16.53
Price at which debentures may be required to be repurchased, percentage of principal and unpaid interest	100.00%
Repayments of convertible debentures				164,300,000
Convertible debentures				166,500,000		2,200,000		2,200,000			262,100,000
Convertible debentures exchanged for shares, value					15,000,000
Convertible debentures exchanged for shares, shares					1,840,000
Amortization expense related to issuance costs	557,000		314,000			200,000	200,000				300,000							100,000	100,000
Interest expense						700,000	800,000				5,600,000
Cash payments for interest	100,000					1,600,000	1,600,000				0		0	0	0
Embedded conversion feature, warrant, conversion ratio											30.2481
Embedded conversion feature, warrant, conversion price (in usd per share)											$ 16.53
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											84 months
Net proceeds from offering										384,300,000
Effective interest rate											8.50%
Long-term debt, balance outstanding														29,600,000
Unamortized discount											134,700,000			400,000
Credit agreement																	100,000,000			125,000,000.0
Debt issuance costs	0		219,000														1,100,000
Borrowing base comprised eligible accounts receivable																		85.00%
Borrowing base comprised eligible accounts inventories																		70.00%
Percentage of total borrowing capacity remaining when convenant takes effect																						30.00%
Letter of credit sub-facility																		50,000,000.0
Basis spread over LIBOR																					2.25%	2.75%
Unused line fee on committed but unutilized commitments																					0.375%	0.50%
Asset-backed revolving credit facility fees recognized																		300,000	200,000
Undrawn letters of credit issued as collateral for sureties																		17,500,000
Capital Lease Obligation
Capital lease obligations incurred during the period		700,000
Capital lease obligations, principal and interest payments	500,000
Interest included in payments	100,000					1,600,000	1,600,000				0		0	0	0
Capital lease obligations	6,000,000
Capitalized Interest
Capitalized interest	$ 800,000		$ 0