Derivative Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative financial instruments
Amount of realized net gain (loss) on derivatives	$ (546)	$ 1,154	$ 333
Foreign currency exchange forwards
Derivative financial instruments
Amount of realized net gain (loss) on derivatives	(89)	248	333
Foreign currency collar
Derivative financial instruments
Amount of realized net gain (loss) on derivatives	(457)	906
Not Designated as Hedges
Derivative financial instruments
Fair value of derivative assets		907
Notional amount of derivative instruments		38,769
Not Designated as Hedges | Foreign currency exchange forwards
Derivative financial instruments
Fair value of derivative assets		1
Notional amount of derivative instruments		4,700
Not Designated as Hedges | Foreign currency collar
Derivative financial instruments
Fair value of derivative assets		906
Notional amount of derivative instruments		$ 34,069