Income Taxes (Components of Loss Before Provision for Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Line Items]
Loss before provision for income taxes	$ (9,858)	$ (9,227)	$ (12,617)	$ (9,688)	$ (15,711)	$ (2,140)	$ (5,442)	$ (7,293)	$ (41,390)	$ (30,587)	$ (16,309)
United States
Income Tax Disclosure [Line Items]
Loss before provision for income taxes									(41,696)	(30,743)	(17,474)
Foreign
Income Tax Disclosure [Line Items]
Loss before provision for income taxes									$ 306	$ 156	$ 1,165