Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2006	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments
Basis of interest rate payments	LIBOR-based
Period during which interest rate payments are likely to occur (in years)	3 years
Contract period of foreign currency forward contracts		3 months	3 months
Fair values and effects of derivatives held
Fair Value, Liability Derivatives		$ (3)	$ (9)
Derivatives not designated as hedging instruments
Fair values and effects of derivatives held
Fair Value, Liability Derivatives		(3)	(9)
Derivatives not designated as hedging instruments | Currency forward contracts
Fair values and effects of derivatives held
Fair Value, Liability Derivatives		$ (3)	$ (9)