Retirement Plans and Other Postretirement Benefits - Summary of Retirement Plans and Other Postretirement Benefits (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Change in plan assets:
Fair value of plan assets at end of year	$ 40,547	$ 34,420
Other Post Retirement Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	2,518	2,344
Service cost	86	82	66
Interest cost	118	116	117
Actuarial (gain) loss	(313)	55
Benefits paid	(79)	(79)
Benefit obligation at end of year	2,330	2,518	2,344
Change in plan assets:
Fair value of plan assets at beginning of year
Actual return on plan assets
Benefits paid	(79)	(79)
Employer contribution and non-qualified benefit payments	79	79
Fair value of plan assets at end of year
Funded status	(2,330)	(2,518)
Unrecognized net actuarial loss	510	850
Unrecognized prior service costs	(7)	(27)
Net amount recognized	(1,827)	(1,695)
Retirement Plans [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	42,879	38,374
Service cost	621	622	556
Interest cost	1,712	1,726	1,725
Actuarial (gain) loss	(3,818)	3,755
Benefits paid	(1,801)	(1,598)
Benefit obligation at end of year	39,593	42,879	38,374
Change in plan assets:
Fair value of plan assets at beginning of year	34,420	25,213
Actual return on plan assets	5,764	2,669
Benefits paid	(1,801)	(1,598)
Employer contribution and non-qualified benefit payments	2,164	8,136
Fair value of plan assets at end of year	40,547	34,420	25,213
Funded status	954	(8,459)
Unrecognized net actuarial loss	14,138	22,576
Unrecognized prior service costs	(1,590)	(1,825)
Net amount recognized	$ 13,502	$ 12,292