Schedule of Reconciliation of Defined Benefit Pension Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Pension Plans And Defined Benefit Postretirement Plans Disclosure [Abstract]
Fair value of plan assets at beginning of year	$ 109,677	$ 106,839
Actual return (loss) on plan assets	15,533	8,858
Benefits paid	(5,846)	(5,651)
Administrative expenses	(697)	(369)
Fair value of plan assets at end of year	118,667	109,677	$ 106,839
Benefit obligation at beginning of year	110,949	118,180
Service cost	721	926	1,051
Interest cost	4,465	4,997
Benefits paid	(5,846)	(5,651)
Actuarial (gain) loss	5,767	(7,503)
Benefit obligation at end of year	116,056	110,949	$ 118,180
Other non-current assets	2,611
Other non-current liabilities		1,272
Total amounts recognized at end of year	$ 2,611	$ (1,272)