Fair Value Measurements - Derivative Liability Contract Measured at Fair Value on a Recurring Basis (Details) (Fair Value Measured on a Recurring Basis, Derivative Liability Contract, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value Measured on a Recurring Basis | Derivative Liability Contract
Derivative Liability Contract Measured at Fair Value on a Recurring Basis Unobservable Input Reconciliation
Balance, beginning of period	$ 383	$ 86
Accruals during the period	0	425
Cash payments during the period	(383)	(128)
Balance, end of period	$ 0	$ 383