Marketable Securities	6 Months Ended
Marketable Securities	Jun. 30, 2021
Marketable Securities [Abstract]
Marketable Securities	Marketable Securities On June 28, 2013, BGC sold certain assets of eSpeed, its on-the-run business, to Nasdaq. The total consideration received by BGC in the transaction included the Nasdaq Earn-out of up to 14,883,705 shares of Nasdaq shares to be paid ratably over 15 years, provided that Nasdaq, as a whole, produces at least $25.0 million in consolidated gross revenues each year. The Nasdaq Earn-out was excluded from the initial gain on the divestiture and is recognized in income as it is realized and earned when these contingent events have occurred, consistent with the accounting guidance for gain contingencies. BGC transferred the remaining rights under the Nasdaq Earn-out to Newmark on September 28, 2017. Any Nasdaq shares that were received by BGC prior to September 28, 2017 were not transferred to Newmark. In connection with the Nasdaq Earn-out, Newmark received 992,247 shares during each of the years ended December 31, 2020 and December 31, 2019. In accordance with the terms of the agreement, Newmark would recognize the remaining Nasdaq Earn-out of up to 6,945,729 shares of Nasdaq shares ratably over approximately the next 7 years, provided that Nasdaq, as a whole, produces at least $25.0 million in gross revenues each year. On February 2, 2021, Nasdaq announced that it entered into a definitive agreement to sell its U.S. fixed income business to Tradeweb. On June 25, 2021, Nasdaq announced the close of the sale of its U.S. fixed income business, which accelerated Newmark’s receipt of Nasdaq shares. Newmark received 6,222,340 Nasdaq shares, with a fair value of $1,093.9 million based on the closing price on June 25, 2021, included in “Other (loss) income, net” on the accompanying unaudited condensed consolidated statement of operations. On June 25, 2021, the SPV notified RBC of its decision to settle the third and fourth Nasdaq Forwards using the Nasdaq shares the SPV received on June 25, 2021. On July 2, 2021, Newmark settled the Nasdaq Forwards with 944,329 Nasdaq shares, with a fair value of $166.0 million based on the closing price of June 30, 2021, and retained 5,278,011 Nasdaq shares. Newmark sold 27,134 and 250,742 of the Nasdaq shares during the three and six months ended June 30, 2021, respectively, and 343,562 for the six months ended June 30, 2020. Newmark did not sell any Nasdaq shares during the three months ended June 30, 2020. The gross proceeds of the Nasdaq shares sold were $3.8 million and $35.4 million for the three and six months ended June 30, 2021, respectively, and $34.6 million for the six months ended June 30, 2020. Newmark recorded realized gains (loss) on the mark-to-market of these securities of $0.7 million and $4.6 million for the three and six months ended June 30, 2021, respectively, and $(2.2) million for the six months ended June 30, 2020. Newmark recorded unrealized gains (loss) on the mark-to-market of these securities of $(14.8) million and $(16.6) million for the three and six months ended June 30, 2021, respectively. Newmark did not record unrealized gains (loss) on the mark-to-market of these securities for the three and six months ended June 30, 2020. Realized and unrealized gains on the mark-to-market of these shares are included in “Other income, net” on the accompanying unaudited condensed consolidated statements of operations. As of June 30, 2021 and December 31, 2020, Newmark had $1,093.9 million and $33.3 million, respectively, included in “Marketable securities” on the accompanying unaudited condensed consolidated balance sheets (see Note 20 — “Securities Loaned”).