Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended		9 Months Ended
	Oct. 21, 2015	Sep. 30, 2015	Dec. 31, 2014	Jun. 26, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Stockholders Equity [Line Items]
Shares repurchased, value							$ 159,471	$ 192,657
Share repurchase remaining authorization		$ 119,461			$ 119,461		$ 119,461
Share repurchase authorization expiration date							Dec. 31, 2016
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
Dividend declared per share of common stock					$ 0.35	$ 0.30	$ 2.00	$ 0.90
Natixis S.A. [Member]
Schedule Of Stockholders Equity [Line Items]
Shares repurchased, shares				1,000,000
Shares repurchased, value				$ 50,340
Series A Preferred Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares outstanding		7,921	7,921		7,921		7,921
Series B Preferred Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares outstanding		0	0		0		0
Class A Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Conversion of Series A preferred stock into Class A common stock (in shares)		0	0
Class A Common Stock [Member] | Subsequent Event [Member]
Schedule Of Stockholders Equity [Line Items]
Dividend declared per share of common stock	$ 0.35
Dividend payable date	Nov. 13, 2015
Dividend date of record	Nov. 02, 2015
Dividend declare date	Oct. 21, 2015