Summary of Significant Accounting Policies (Cash and Equivalents) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 138,144	$ 32,335	$ 34,473	$ 119,471
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	5,682	4,481
Money market funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	71,205	20,354
Government-backed security [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	28,000	7,500
Corporate debt securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	29,196	0
Asset-backed Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 4,061	$ 0