Summary of Significant Accounting Policies (Cash and Equivalents) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 167,384	$ 32,335	$ 103,857	$ 119,471
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	13,203	4,481
Money market funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	125,090	20,354
Government-backed security [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	28,000	7,500
Asset-backed Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 1,091	$ 0