Stock-Based Compensation Plans and Employee Benefits - Summary of Fair Values for Stock-based Awards Granted Using Black-Scholes Option Pricing Model (Detail) - Black-Scholes Option Pricing Model [Member]	12 Months Ended
	Dec. 31, 2017 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value of grants	$ 2.07
Risk-free interest rate (range) - Based upon the U.S. Treasury Strip with a maturity date that approximates the expected term of the award	1.80%
Dividend yield (range) – Forecasted dividend yield based on the expected life	5.20%
Expected life (range) – Derived by referring to actual exercise experience	4 years
Expected volatility (range) - Derived by using a 50/50 blend of implied and historical changes in the Company's historical stock prices over a time frame consistent with the expected life of the award	19.80%