Debt and Capital Lease Obligation (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended				3 Months Ended	6 Months Ended		0 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Oct. 31, 2009 1.875% Convertible debentures [Member]	Jun. 30, 2012 1.875% Convertible debentures [Member]	Jun. 30, 2011 1.875% Convertible debentures [Member]	Jun. 30, 2012 1.875% Convertible debentures [Member]	Jun. 30, 2011 1.875% Convertible debentures [Member]	Dec. 31, 2011 1.875% Convertible debentures [Member]	Mar. 12, 2008 1.875% Convertible debentures [Member]	Jun. 30, 2012 8% Series 2000 [Member]	Jun. 30, 2012 8% Series 2000 [Member]	Dec. 31, 2011 8% Series 2000 [Member]	Dec. 23, 2011 Credit Agreement [Member]	Jun. 30, 2012 Credit Agreement [Member]	Jun. 30, 2012 Credit Agreement [Member]	Jan. 13, 2012 Credit Agreement [Member]	Jun. 30, 2012 Credit Agreement [Member] Minimum [Member]	Jun. 30, 2012 Credit Agreement [Member] Maximum [Member]
Debt Instrument [Line Items]
Aggregate principal amount of senior convertible debentures											$ 181,500,000
Debt, face value												30,000,000	30,000,000	30,000,000
Debt instrument interest rate						1.875%		1.875%		1.875%		8.00%	8.00%	8.00%
Debt maturity date								Mar. 15, 2028					Jul. 01, 2020
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
Debt conversion price (in usd per share)						$ 23.51		$ 23.51
Convertible debentures exchanged for shares, value					15,000,000
Convertible debentures exchanged for shares, shares					1,840,000
Long-term debt obligations converted to short-term debt obligations						166,500,000		166,500,000
Amortization expense related to issuance costs	315,000	246,000	629,000	491,000		200,000	200,000	500,000	500,000							100,000
Interest expense on the debentures						800,000	800,000	1,600,000	1,600,000
Long-term debt, balance outstanding												29,500,000	29,500,000
Unamortized discount												500,000	500,000
Cash payments for interest						1,600,000	1,600,000					1,200,000
Credit agreement															100,000,000			125,000,000
Debt issuance costs	0	0	219,000	0											1,100,000
Borrowing base comprised eligible accounts receivable																	85.00%
Borrowing base comprised eligible accounts inventories																	70.00%
Percentage of Debt When Covenant Takes Effect																				30.00%
Letter of Credit, Capacity																50,000,000	50,000,000
Debt Instrument, Basis Spread on Variable Rate																			2.25%	2.75%
Debt Instrument Fee Percent																			(0.375%)	0.50%
Asset-backed revolving credit agreement fee																200,000	200,000
Undrawn letters of credit issued as collateral for sureties																5,300,000	5,300,000
Capital Lease Obligation
Capital lease obligations	6,700,000		6,700,000
Capitalized Interest
Capitalized interest			$ 600,000