Incentive Plans - Summary of LFI and Other Similar Deferred Compensation Arrangements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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	(93)	(340)
Prepaid Compensation Asset, Amortization	(12,491)	(19,436)
Prepaid Compensation Asset, Other	(12)	132
Prepaid Compensation Asset, Ending Balance	114,634	107,930
Compensation Liability, Beginning Balance	170,388	193,574
Compensation Liability, Granted	77,580	51,871
Compensation Liability, Settled	(81,559)	(64,488)
Compensation Liability, Forfeited	(133)	(681)
Compensation Liability, Increase (Decrease) in fair value of underlying investments	7,353	(2,514)
Compensation Liability, Adjustment for estimated forfeitures	532	1,804
Compensation Liability, Other	579	913
Compensation Liability, Ending Balance	$ 174,740	$ 180,479