Summary of Significant Accounting Policies (Cash and Equivalents) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 103,857	$ 119,471	$ 2,574	$ 17,399
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	2,789	4,251
Money market funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	73,069	100,049
Government-backed security [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	18,000
Corporate Debt Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 9,999	$ 15,171