Stock Transactions and Unit Redemptions - Additional Information (Detail)			1 Months Ended	12 Months Ended
	Nov. 23, 2018 USD ($) shares	Mar. 09, 2018 USD ($)	Nov. 30, 2014 shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 shares	Aug. 01, 2018 USD ($)	Mar. 31, 2018 shares
Class of Stock [Line Items]
Number of shares, right to exchange from Class A to Class B common stock					11,036,273
Limited Partnership Units Exchange Ratio				1
Common stock, issued during the period, additional consideration | $	$ 0
Payment percentage of the gross proceeds from the sale of shares			2.00%
Stock repurchase program and unit redemption remaining authorized amount | $				$ 256,691,000
Class B Common Stock [Member]
Class of Stock [Line Items]
Limited Partnership Units Exchange Ratio	1
Common stock, issued during the period				0
Common stock outstanding				45,884,380	45,884,380
Common stock, shares issued				45,884,000	45,884,000
Common stock value issued | $				$ 459,000	$ 459,000
Class A Common Stock [Member]
Class of Stock [Line Items]
Number of shares, right to exchange from Class A to Class B common stock					11,036,000
Common stock, issued during the period				212,711	26,003,424	1,994,670
Common stock outstanding				307,915,000	291,475,000
Common stock, shares issued				358,440,000	341,745,000
Common stock value issued | $				$ 3,584,000	$ 3,417,000
Company's repurchase and additional redemption authority amount | $							$ 300,000,000.0
Stock repurchase program and unit redemption remaining authorized amount | $				$ 256,700,000
Class A Common Stock [Member] | November 2014 Sales Agreement [Member]
Class of Stock [Line Items]
Maximum number of shares under the controlled equity offering			20,000,000
Class A Common Stock [Member] | CEO Program [Member]
Class of Stock [Line Items]
Common stock, shares issued						20,000,000		20,000,000
Class A Common Stock [Member] | New CEO Program [Member]
Class of Stock [Line Items]
Common stock, shares issued				17,401,431
Maximum amount under the controlled equity offering program | $		$ 300,000,000.0
Common stock value issued | $				$ 209,800,000
Cantor [Member] | Class B Common Stock [Member]
Class of Stock [Line Items]
Number of shares, right to exchange from Class A to Class B common stock	10,323,366
CFGM [Member] | Class B Common Stock [Member]
Class of Stock [Line Items]
Number of shares, right to exchange from Class A to Class B common stock	712,907
Cantor or CFGM [Member] | Class B Common Stock [Member]
Class of Stock [Line Items]
Common stock, issued during the period, additional consideration | $	$ 0