Fair Value Measurements (Details 1) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value
Cash and Cash Equivalents	$ 83,293	$ 46,600
Short-term Investments	113,524	299,904
Total Cash and Cash Equivalents and Investments	196,817	346,504
Accrued Liabilities		18,912
Total Liabilities		18,912
Fair Value, Level 1
Fair Value
Cash and Cash Equivalents	83,293	45,093
Short-term Investments	90,476	227,805
Total Cash and Cash Equivalents and Investments	173,769	272,898
Accrued Liabilities		0
Total Liabilities		0
Fair Value, Level 2
Fair Value
Cash and Cash Equivalents	0	1,507
Short-term Investments	23,048	72,099
Total Cash and Cash Equivalents and Investments	23,048	73,606
Accrued Liabilities		0
Total Liabilities		0
Fair Value, Level 3
Fair Value
Cash and Cash Equivalents	0	0
Short-term Investments	0	0
Total Cash and Cash Equivalents and Investments	$ 0	0
Accrued Liabilities		18,912
Total Liabilities		$ 18,912