Quarterly report pursuant to Section 13 or 15(d)

Cash and cash equivalents

Cash and cash equivalents
9 Months Ended
Sep. 30, 2018
Cash, Cash Equivalents, and Short-term Investments [Abstract]  
Cash and cash equivalents Cash and cash equivalentsAll highly liquid investments with maturities of three months or less at the date of purchase are classified as cash equivalents. As of September 30, 2018 and December 31, 2017, the amount of cash and cash equivalents was $45.6 million and $137.0 million, respectively and consists of checking accounts and short-term U.S. Treasury money market mutual funds. Checking accounts are held at U.S. commercial banks, and balances were in excess of the FDIC insurance limit.