Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value, Total	$ 95,847	$ 144,353	$ 132,225	$ 93,108
Cash and Cash Equivalents [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value, Total	3,500
Cash and Cash Equivalents [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value, Total	$ 5,991	$ 11,976