Annual report pursuant to Section 13 and 15(d)

Cash, Cash Equivalents, and Short-term Investments - Schedule of cash, cash equivalents and short-term investments (Details)

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Cash, Cash Equivalents, and Short-term Investments - Schedule of cash, cash equivalents and short-term investments (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Cash and cash equivalents:        
Cash and Cash Equivalents, at Carrying Value $ 213,551 $ 82,469 $ 66,558 $ 56,106
Short-term investments:        
Total short-term investment 34,019 0    
Total cash, cash equivalents and short-term investments 247,570 82,469    
U.S. investment grade bonds        
Short-term investments:        
Total short-term investment 24,477 0    
Developed investment grade bonds        
Short-term investments:        
Total short-term investment $ 9,542 $ 0