Quarterly report pursuant to Section 13 or 15(d)

Cash Equivalents and Marketable Securities - Components of Cash Equivalents and Marketable Securities (Details)

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Cash Equivalents and Marketable Securities - Components of Cash Equivalents and Marketable Securities (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Sep. 30, 2019
Sep. 30, 2018
Cash Equivalents and Marketable Securities [Line Items]      
Cash and cash equivalents $ 53,039 $ 92,143 $ 54,225
Equity securities 563    
Equity securities, gross unrealized gains 25    
Equity securities, gross unrealized losses 0    
Equity securities, estimated fair value 588    
Adjusted Cost 31,788    
Estimated Fair Value 31,813    
Money Market Funds [Member]      
Cash Equivalents and Marketable Securities [Line Items]      
Cash and cash equivalents 31,225 73,450  
Cash and cash equivalents, fair value 31,225 73,450  
Estimated Fair Value $ 31,200 $ 73,500