Retirement Plans and Other Postretirement Benefits - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Employee hire date no longer eligible for noncontributory retirement plan	Dec. 08, 2009
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, non-qualified plans, estimated employer contributions for next fiscal year		$ 162
Defined benefit plan, contributions by employer	90
Defined benefit plan, benefits paid	1,500
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions for next fiscal year		94
Defined benefit plan, contributions by employer	69
Defined benefit plan, benefits paid	$ 69