Incentive Plans - Summary of LFI and Other Similar Deferred Compensation Arrangements (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Deferred Compensation Arrangements [Abstract]
Prepaid Compensation Asset, Beginning Balance	$ 49,650	$ 75,703
Prepaid Compensation Asset, Granted	77,580	51,871
Prepaid Compensation Asset, Forfeited	(585)	(704)
Prepaid Compensation Asset, Amortization	(39,503)	(37,890)
Prepaid Compensation Asset, Other	942	(873)
Prepaid Compensation Asset, Ending Balance	88,084	88,107
Compensation Liability, Beginning Balance	170,388	193,574
Compensation Liability, Granted	77,580	51,871
Compensation Liability, Settled	(95,633)	(68,628)
Compensation Liability, Forfeited	(933)	(1,228)
Compensation Liability, Increase (Decrease) in fair value of underlying investments	13,106	(2,202)
Compensation Liability, Adjustment for estimated forfeitures	2,138	3,385
Compensation Liability, Other	1,312	357
Compensation Liability, Ending Balance	$ 167,958	$ 177,129