Basis of Presentation - Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Balance as of December 31, 2012			$ 13,286
Foreign currency translation adjustments during period	86	(503)	(1,294)	161
Unrealized gain (loss) on investments during period	(3,546)	(5,395)	(8,404)	(4,412)
Current period other comprehensive loss	(3,460)	(5,898)	(9,698)	(4,251)
Balance as of June 30, 2013	3,588		3,588
Foreign Currency Translation Adjustments
Balance as of December 31, 2012			1,055
Foreign currency translation adjustments during period			(1,294)
Balance as of June 30, 2013	(239)		(239)
Unrealized Gain (Loss) on Investments
Balance as of December 31, 2012			12,231
Unrealized gain (loss) on investments during period			(8,404)
Balance as of June 30, 2013	3,827		3,827
Accumulated Other Comprehensive Income
Balance as of December 31, 2012			13,286
Current period other comprehensive loss			(9,698)
Balance as of June 30, 2013	$ 3,588		$ 3,588