Pension and Employee Benefit Plans - Components of Pension and Employee Benefit Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 415	$ 447	$ 233
Interest cost	1,314	1,426	1,412
Expected return on plan assets	(1,723)	(1,829)	(2,009)
Net amortization and deferral	227	212	258
Net periodic benefit cost (income)	$ 233	$ 256	$ (106)