Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Accumulated Other Comprehensive (Income) Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net gain	$ (739)	$ (130)
Amortization of prior service cost	0	0
Amortization of net obligation at transition	0	0
Total recognized in other comprehensive loss (income)	(739)	(130)
Total recognized in net periodic benefit cost and other comprehensive loss (income)	(325)	100
PRB Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net gain	(10)	(109)
Amortization of prior service cost	0	0
Amortization of net obligation at transition	0	0
Total recognized in other comprehensive loss (income)	(10)	(109)
Total recognized in net periodic benefit cost and other comprehensive loss (income)	$ (380)	$ (77)