Schedule I - Parent Company Only Financial Statements - Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income available to common stockholders	$ 70,924	$ 23,864	$ 20,137
Adjustments to reconcile net income to net cash used in operating activities:
Losses on equity investments	9,508	11,775	6,605
Deferred tax (benefit) expense	(81,989)	(11,550)	1,963
Decrease (increase) in operating assets:
Receivables from related parties	(5,362)	(14,726)	(2,447)
Other assets	(73,422)	(2,046)	(10,413)
(Decrease) increase in operating liabilities:
Accounts payable, accrued and other liabilities	145,167	23,371	(15,438)
Payables to related parties	(24,862)	21,000	9,405
Net cash provided by operating activities	166,366	171,200	85,344
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(746)	(31,413)	(46,703)
Purchase of notes receivable		(22,000)
Distribution from equity method investment		928
Net cash provided by (used in) investing activities	526,753	(67,983)	(92,646)
CASH FLOWS FROM FINANCING ACTIVITIES:
Dividends to stockholders	(91,395)	(90,590)	(77,244)
Repurchase of Class A common stock	(15,528)	(337)	(392)
Issuance of convertible notes			155,620
Purchase of capped call			(11,392)
Repayments of collateral borrowings	(48,246)	(24,778)	(17,272)
Repayments of short-term borrowings		(103,600)	(16,400)
Proceeds from offering of Class A common stock, net		12,667	15,632
Proceeds from exercises of stock options			8,812
Other	32	32	63
Net cash (used in) provided by financing activities	(363,343)	(85,008)	8,621
Net increase in cash and cash equivalents	328,510	18,696	5,609
Cash and cash equivalents at beginning of period	388,409	369,713	364,104
Cash and cash equivalents at end of period	716,919	388,409	369,713
Supplemental non-cash information
Issuance of Class A common stock upon exchange of Cantor units			8,407
Issuance of Class B common stock upon exchange of Cantor units			8,407
Issuance of Class A common stock upon exchange of limited partnership interests	65,908	90,199	79,115
Issuance of Class A and contingent Class A common stock for acquisitions	1,776	9,026	26,778
Use of notes receivable in business acquisition		25,617
Parent Company [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income available to common stockholders	70,924	23,864	20,137
Adjustments to reconcile net income to net cash used in operating activities:
Losses on equity investments	(186,868)	(32,441)	(24,083)
Deferred tax (benefit) expense	(52,549)	(8,839)	2,394
Decrease (increase) in operating assets:
Receivables from related parties	(92,044)	52,828	(12,954)
Note receivable from related party	11,940	(97,851)	(139,413)
Other assets	(1,425)	(5,782)	(1,557)
(Decrease) increase in operating liabilities:
Accounts payable, accrued and other liabilities	39,295	16,799	11,928
Payables to related parties	112,207	41,063	60,227
Net cash provided by operating activities	(98,520)	(10,359)	(83,321)
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(230)	(30,153)	(61,829)
Purchase of notes receivable		(22,000)
Distribution from equity method investment		928
Net cash provided by (used in) investing activities	(230)	(51,225)	(61,829)
CASH FLOWS FROM FINANCING ACTIVITIES:
Dividends to stockholders	(91,395)	(90,590)	(77,244)
Repurchase of Class A common stock	(15,528)	(337)	(392)
Issuance of convertible notes			155,620
Purchase of capped call			(11,392)
Proceeds from long-term borrowings		108,716
Proceeds from collateralized borrowings			4,986
Repayments of collateral borrowings	(11,940)	(10,865)	(9,801)
Proceeds from short-term borrowings		90,000	30,000
Repayments of short-term borrowings		(103,600)	(16,400)
Distributions from subsidiaries	171,980	55,537	45,187
Proceeds from offering of Class A common stock, net	45,673	12,667	15,632
Proceeds from exercises of stock options			8,812
Other		83	90
Net cash (used in) provided by financing activities	98,790	61,611	145,098
Net increase in cash and cash equivalents	40	27	(52)
Cash and cash equivalents at beginning of period	27		52
Cash and cash equivalents at end of period	67	27
Supplemental non-cash information
Issuance of Class A common stock upon exchange of Cantor units			8,407
Issuance of Class B common stock upon exchange of Cantor units			8,407
Issuance of Class A common stock upon exchange of limited partnership interests	65,908	90,199	79,115
Issuance of Class A and contingent Class A common stock for acquisitions	1,776	9,026	26,778
Donations with respect to Charity Day	5,720	13,401	12,076
Issuance of Class A common stock upon purchase of notes receivable		3,055
Use of notes receivable in business acquisition		$ 25,617