Schedule I - Condensed Statements of Cash Flows (Parent Company Only) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
NET INCOME	$ 157,786	$ 398,521	$ 374,113	$ 55,953	$ 172,384	$ 88,859	$ 85,192	$ 80,842	$ 986,373	$ 427,277	$ 160,212
Adjustments to reconcile net income to net cash provided by operating activities:
Net cash provided by operating activities									887,296	736,017	526,697
CASH FLOWS FROM FINANCING ACTIVITIES:
Class A common stock dividends									(290,684)	(146,241)	(121,620)
Net cash used in financing activities									(746,804)	(435,369)	(487,072)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS									65,503	225,098	(8,708)
CASH AND CASH EQUIVALENTS-January 1				1,066,580				841,482	1,066,580	841,482	850,190
CASH AND CASH EQUIVALENTS-December 31	1,132,083				1,066,580				1,132,083	1,066,580	841,482
Parent Company [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
NET INCOME									986,373	427,277	160,212
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries									(931,036)	(373,713)	(103,769)
Changes in due to/from subsidiaries									233,519	99,477	65,574
Changes in other operating assets and liabilities									250	(6)	(7)
Net cash provided by operating activities									289,106	153,035	122,010
CASH FLOWS FROM FINANCING ACTIVITIES:
Class A common stock dividends									(290,684)	(146,241)	(121,620)
Net cash used in financing activities									(290,684)	(146,241)	(121,620)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS									(1,578)	6,794	390
CASH AND CASH EQUIVALENTS-January 1				$ 7,482				$ 688	7,482	688	298
CASH AND CASH EQUIVALENTS-December 31	$ 5,904				$ 7,482				$ 5,904	$ 7,482	$ 688