Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 3,000		$ 4,300
Proceeds from sale/maturity of short-term investments	$ 104,291	$ 61,833
Maximum
Summary Of Significant Accounting Policies [Line Items]
Short-term investment contractual maturities	2 years		2 years