Summary of Significant Accounting Policies (Cash and Equivalents) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 109,921	$ 119,471	$ 9,023	$ 17,399
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	3,944	4,251
Money market funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	95,977	100,049
U.S. treasury security [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	10,000
Corporate Debt Securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents		$ 15,171