Employee Benefit Plans - Summary of Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Income (Detail) - USD ($) |
12 Months Ended | |
---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
|
Pension Plan [Member] | ||
Net periodic benefit cost | ||
Interest cost | $ 2,958,903 | $ 530,839 |
Expected return on plan assets | (3,562,150) | (1,000,732) |
Recognized actuarial (gain) loss due to settlements | (636,121) | |
Net periodic benefit cost | (1,239,368) | (469,893) |
Supplemental Employee Retirement Plan [Member] | ||
Net periodic benefit cost | ||
Interest cost | 340,262 | 51,696 |
Net periodic benefit cost | 340,262 | 51,696 |
Postretirement Benefits [Member] | ||
Net periodic benefit cost | ||
Service cost | 11,860 | 8,169 |
Interest cost | 26,269 | 11,097 |
Recognized actuarial (gain) loss | (2,079) | |
Curtailment charge (credit) | (1,678,920) | |
Recognized actuarial (gain) loss due to settlements | (169,089) | |
Net periodic benefit cost | $ (1,811,959) | $ 19,266 |