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Cash, Cash Equivalents and Marketable Securities (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Cash, Cash Equivalents and Marketable Securities    
Cash, cash equivalents and marketable securities, Unrealized gains $ 64 $ 25
Carrying value    
Cash, Cash Equivalents and Marketable Securities    
Cash and cash equivalents 8,215 19,145
Total cash, cash equivalents and marketable securities 40,063 40,475
Fair value    
Cash, Cash Equivalents and Marketable Securities    
Cash and cash equivalents 8,215 19,145
Total cash, cash equivalents and marketable securities $ 40,127 $ 40,500
Corporate debt securities due within 1 year of date of purchase    
Cash, Cash Equivalents and Marketable Securities    
Maturity period from date of purchase to classify an investment as marketable securities 1 year 1 year
Corporate debt securities due within 1 year of date of purchase | Level 2    
Cash, Cash Equivalents and Marketable Securities    
Marketable securities, unrealized gains $ 64 $ 25
Corporate debt securities due within 1 year of date of purchase | Carrying value | Level 2    
Cash, Cash Equivalents and Marketable Securities    
Marketable securities, cost 31,848 21,330
Corporate debt securities due within 1 year of date of purchase | Fair value | Level 2    
Cash, Cash Equivalents and Marketable Securities    
Marketable securities, fair value $ 31,912 $ 21,355
Corporate debt securities due within 3 months of date of purchase    
Cash, Cash Equivalents and Marketable Securities    
Maturity period from date of purchase to classify an investment as marketable securities 3 months 3 months
Cash | Carrying value | Level 1    
Cash, Cash Equivalents and Marketable Securities    
Cash and cash equivalents $ 1,911 $ 5,651
Cash | Fair value | Level 1    
Cash, Cash Equivalents and Marketable Securities    
Cash and cash equivalents 1,911 5,651
Money market funds | Carrying value | Level 1    
Cash, Cash Equivalents and Marketable Securities    
Cash and cash equivalents 6,304 13,494
Money market funds | Fair value | Level 1    
Cash, Cash Equivalents and Marketable Securities    
Cash and cash equivalents $ 6,304 $ 13,494