Fair Value Measurements - Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan investments	$ 25,055	$ 22,204
Total assets measured at fair value	25,055	22,204
Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan investments	25,055	22,204
Total assets measured at fair value	$ 25,055	$ 22,204