Incentive Plans - Summary of Impact of LFI and Other Similar Deferred Compensation Arrangements (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation [Abstract]
Amortization, net of forfeitures	$ 73,382	$ 75,573	$ 85,563
Change in the fair value of underlying investments	23,526	3,318	(3,827)
Total	$ 96,908	$ 78,891	$ 81,736

Amount of expense recognized from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments), awarded to key employees or individuals. Excludes amount related to plans that cover generally all employees (for example, but not limited to, qualified pension plans).

No definition available.

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