Fair Value Measurements - Fair Value of Other Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Carrying Value [Member] | Capital Lease Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Capital lease obligations	$ 1,944		$ 1,784
Fair Value [Member] | Capital Lease Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Capital lease obligations	1,863		1,736
2008 Notes [Member] | Carrying Value [Member] | Convertible Debt [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	0	[1]	5,133	[1]
2008 Notes [Member] | Fair Value [Member] | Convertible Debt [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	0	[1]	5,163	[1]
2012 Term Loan [Member] | Carrying Value [Member] | Term loan [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	24,405		25,000
2012 Term Loan [Member] | Fair Value [Member] | Term loan [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt	$ 24,405		$ 25,000

[1] The carrying value of the 2008 Notes represents the discounted debt component only, while the fair value of the Notes is based on the market value of the respective notes, including convertible equity features.