Pension and Employee Benefit Plans - Disclosure of Fair Value Measurements of Pension Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	$ 26,836	$ 24,063
Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	18,723	16,153
Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	6,967	7,016
Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	26,836	24,063
Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	18,723	16,153
Level 1 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	6,967	7,016
Cash and cash equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	1,147	894
Cash and cash equivalents [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Pension assets, at fair value	$ 1,147	$ 894