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Cash Collateral Pledged	3 Months Ended
Cash Collateral Pledged	Mar. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash Collateral Pledged	Cash Collateral Pledged As of March 31, 2018 and December 31, 2017, the Company pledged cash collateral in the amount of $5.9 million and $6.1 million, respectively, which relates to letters of credit issued to the landlords of the Company's premises in New York City, Boston, Stamford and San Francisco. The Company also has pledged as collateral, $8.9 million, as of March 31, 2018, and $11.8 million, as of December 31, 2017, anticipated to be due March 2021, for reinsurance agreements (see Note 17).