Summary of Significant Accounting Policies - Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Balance as of December 31, 2012	$ 13,286
Foreign currency translation adjustments	160	857
Unrealized gain (loss) on investments during period	(4,626)	2,426
Current period other comprehensive income (loss)	(4,466)	3,283
Balance as of December 31, 2013	8,820	13,286
Foreign Currency Translation Adjustments
Balance as of December 31, 2012	1,055
Foreign currency translation adjustments	160
Balance as of December 31, 2013	1,215
Unrealized Gain (Loss) on Investments
Balance as of December 31, 2012	12,231
Unrealized gain (loss) on investments during period	(4,626)
Balance as of December 31, 2013	7,605
Accumulated Other Comprehensive Income
Balance as of December 31, 2012	13,286
Foreign currency translation adjustments	160	857
Unrealized gain (loss) on investments during period	(4,626)	2,426
Current period other comprehensive income (loss)	(4,466)
Balance as of December 31, 2013	$ 8,820	$ 13,286