Summary of Significant Accounting Policies (Details 1) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Carrying value and estimated fair value of debt
Carrying value of debt	$ 272,247,000	$ 274,698,000
Carrying Value | Credit Agreement Debt
Carrying value and estimated fair value of debt
Carrying value of debt	146,000,000	150,000,000
Carrying Value | Convertible Debt
Carrying value and estimated fair value of debt
Carrying value of debt (par value)	150,000,000	150,000,000
Fair Value | Credit Agreement Debt
Carrying value and estimated fair value of debt
Debt Instrument, Fair value	158,000,000	163,000,000
Fair Value | Convertible Debt
Carrying value and estimated fair value of debt
Debt Instrument, Fair value	$ 167,000,000	$ 158,000,000