Schedule I - Condensed Statements of Financial Condition (Parent Company Only) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Cash and cash equivalents	$ 1,158,785	$ 1,132,083	$ 1,066,580	$ 841,482
Investments in subsidiaries, equity method	222	8,917
Other assets	184,499	217,022
Total Assets	4,556,508	4,477,774	3,325,329
Liabilities:
Other liabilities	530,241	499,942
Total Liabilities	3,262,695	3,110,468
Commitments and contingencies
Common stock:
Class A, par value $.01 per share (500,000,000 shares authorized; 129,766,091 shares issued at December 31, 2016 and 2015, including shares held by subsidiaries as indicated below)	1,298	1,298
Additional paid-in-capital	688,231	600,034
Retained earnings	1,134,186	1,123,728
Accumulated other comprehensive loss, net of tax	(314,222)	(234,356)	(200,766)	(133,004)
Stockholders' equity subtotal before common stock held by subsidiaries and Noncontrolling interests, total	1,509,493	1,490,704
Class A common stock held by subsidiaries, at cost (7,628,786 and 4,253,381 shares at December 31, 2016 and 2015, respectively)	(273,506)	(177,249)
Total stockholders’ equity	1,235,987	1,313,455
Total Liabilities and Stockholders’ Equity	4,556,508	4,477,774
Series A Preferred Stock [Member]
Preferred stock:
Preferred stock
Series B Preferred Stock [Member]
Preferred stock:
Preferred stock
Parent Company [Member]
ASSETS
Cash and cash equivalents	3,916	5,904	$ 7,482	$ 688
Investments in subsidiaries, equity method	(534,642)	(747,753)
Due from subsidiaries	1,766,875	2,055,748
Other assets	13
Total Assets	1,236,162	1,313,899
Liabilities:
Due to subsidiaries	65	113
Other liabilities	110	331
Total Liabilities	175	444
Commitments and contingencies
Common stock:
Class A, par value $.01 per share (500,000,000 shares authorized; 129,766,091 shares issued at December 31, 2016 and 2015, including shares held by subsidiaries as indicated below)	1,298	1,298
Additional paid-in-capital	688,231	600,034
Retained earnings	1,134,186	1,123,728
Accumulated other comprehensive loss, net of tax	(314,222)	(234,356)
Stockholders' equity subtotal before common stock held by subsidiaries and Noncontrolling interests, total	1,509,493	1,490,704
Class A common stock held by subsidiaries, at cost (7,628,786 and 4,253,381 shares at December 31, 2016 and 2015, respectively)	(273,506)	(177,249)
Total stockholders’ equity	1,235,987	1,313,455
Total Liabilities and Stockholders’ Equity	1,236,162	1,313,899
Parent Company [Member] | Series A Preferred Stock [Member]
Preferred stock:
Preferred stock
Parent Company [Member] | Series B Preferred Stock [Member]
Preferred stock:
Preferred stock