XML 104 R92.htm IDEA: XBRL DOCUMENT v3.19.1
Incentive Plan - Summary of Fair Value of Stock Options Granted (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Risk-free interest rate 2.65% 2.31% 1.69%
Expected option life 7 years 7 years 7 years
Expected volatility 21.00% 21.00% 21.00%
Expected dividend yield 2.19% 2.07% 3.01%
Weighted average fair value of an option share granted during the year $ 5.44 $ 5.62 $ 2.64
Intrinsic value of options exercised during the year $ 8,513 $ 7,882 $ 3,412