Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended								12 Months Ended
	Feb. 01, 2017	Jun. 26, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Stockholders Equity [Line Items]
Common stock held by subsidiaries, shares			7,628,786				4,253,381				7,628,786	4,253,381
Shares repurchased, value											$ 300,217	$ 172,772	$ 192,657
Purchase of Class A common stock (in shares)											8,551,271	3,438,789	4,114,206
Share repurchase remaining authorization			$ 355,125								$ 355,125
Preferred stock, shares authorized			15,000,000				15,000,000				15,000,000	15,000,000
Preferred stock, par value			$ 0.01				$ 0.01				$ 0.01	$ 0.01
Conversion of Series A preferred stock into Class A common stock												0
Dividend declared per share of common stock			$ 0.38	$ 0.38	$ 0.38	$ 1.55	$ 0.35	$ 0.35	$ 0.35	$ 1.30	$ 2.69	$ 2.35	$ 1.20
Subsequent Event [Member]
Schedule Of Stockholders Equity [Line Items]
Dividend declared per share of common stock	$ 0.38
Special dividend declared per share of common stock	$ 1.20
Dividend payable date	Feb. 24, 2017
Dividend date of record	Feb. 13, 2017
Dividend declare date	Feb. 01, 2017
January and April, 2016 [Member]
Schedule Of Stockholders Equity [Line Items]
Share repurchase remaining authorization			$ 119,125								$ 119,125
Share repurchase authorization expiration date											Dec. 31, 2017
November, 2016 [Member]
Schedule Of Stockholders Equity [Line Items]
Share repurchase remaining authorization			$ 236,000								$ 236,000
Share repurchase authorization expiration date											Dec. 31, 2018
Class A Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Common stock held by subsidiaries, shares			7,628,786				4,253,381				7,628,786	4,253,381
Series A Preferred Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares outstanding			0				7,921				0	7,921
Series B Preferred Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares outstanding			0				0				0	0
LAZ-MD Holdings LLC [Member]
Schedule Of Stockholders Equity [Line Items]
Shares in exchanges of a like number of common membership interests													710,009
Executive Officers [Member] | Class A Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Shares repurchased, value											$ 4,900	$ 17,700	$ 6,800
Natixis S.A. [Member]
Schedule Of Stockholders Equity [Line Items]
Shares repurchased, value		$ 50,340
Purchase of Class A common stock (in shares)		1,000,000