Borrowing Arrangements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
2010 Convertible Senior Subordinated Notes [Member]
Summary of carrying amount of the debt and equity components
Principal amount of notes	$ 130,000	$ 130,000
Unamortized discount	(7,650)	(8,334)
Net carrying amount	122,350	121,666
Additional paid-in-capital, net of tax	8,555	8,555
2006 Convertible Senior Subordinated Notes [Member]
Summary of carrying amount of the debt and equity components
Principal amount of notes	750	750
Unamortized discount
Net carrying amount	750	750
Additional paid-in-capital, net of tax	$ 11,425	$ 11,425

Adjustment to additional paid in capital resulting from the recognition of convertible debt instruments as two separate components - a debt component and an equity component. This bifurcation may result in a basis difference associated with the liability component that represents a temporary difference for purposes of applying accounting for income taxes. The initial recognition of deferred taxes for the tax effect of that temporary difference is as an adjustment to additional paid in capital.

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Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date before deducting unamortized discount or premiums (if any). May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer.

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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