Fair Value Measurements (Details 1) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value
Cash and Cash Equivalents	$ 45,778	$ 80,386
Short-term Investments	87,367	79,666
Total Cash and Cash Equivalents and Investments	133,145	160,052
Fair Value, Level 1
Fair Value
Cash and Cash Equivalents	45,778	80,386
Short-term Investments	87,367	73,974
Total Cash and Cash Equivalents and Investments	133,145	154,360
Fair Value, Level 2
Fair Value
Cash and Cash Equivalents	0	0
Short-term Investments		5,692
Total Cash and Cash Equivalents and Investments	0	5,692
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