Benefit Plans - Benefit Obligation and Plan Asset Rollforward (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in plan assets:
Fair value of plan assets at beginning of year	$ 42,744
Fair value of plan assets at end of year	41,448	$ 42,744
Pension [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	28,921	28,605	$ 32,189
Service cost	0	0	0
Interest cost	1,137	1,271	1,273
Actuarial loss (gain)	78	51	114
Benefits paid	(1,179)	(5,326)	(969)
Change in actuarial assumptions	(683)	4,320	(4,002)
Benefit obligation at end of year	28,274	28,921	28,605
Change in plan assets:
Fair value of plan assets at beginning of year	42,744	45,202	40,072
Actual return on plan assets	(117)	2,868	6,099
Employer contributions	0	0	0
Benefits paid	(1,179)	(5,326)	(969)
Fair value of plan assets at end of year	41,448	42,744	45,202
Funded status at end of year	13,174	13,823	16,597
Post-retirement [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	28,333	22,086	25,116
Service cost	168	169	240
Interest cost	1,122	1,087	981
Actuarial loss (gain)	122	51	(210)
Benefits paid	(644)	(670)	(624)
Change in actuarial assumptions	(3,407)	5,610	(3,417)
Benefit obligation at end of year	25,694	28,333	22,086
Change in plan assets:
Fair value of plan assets at beginning of year	0	0	0
Actual return on plan assets	0	0	0
Employer contributions	644	670	624
Benefits paid	(644)	(670)	(624)
Fair value of plan assets at end of year	0	0	0
Funded status at end of year	$ (25,694)	$ (28,333)	$ (22,086)