Changes in Accumulated Other Comprehensive Income (Loss) (Additional Information) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Actuarial gains losses, net of tax	$ (6,100,000)		$ 5,900,000		$ (3,600,000)
Actuarial gains losses, tax portion	3,700,000		(3,600,000)		2,100,000
Amortization of actuarial losses, net of tax	3,496,000	[1]	663,000	[1]	569,000	[1]
Amortization of actuarial losses, tax portion	2,100,000		400,000		300,000
Pension settlement costs, net of tax	3,000,000
Pension settlement costs, tax portion	$ 1,900,000

[1] (b) Amount represents the amortization of actuarial losses to pension expense arising from the Company’s postretirement benefit obligation. This amount was $3.5 million, net of $2.1 million tax benefit, which included $3.0 million, net of $1.9 million tax benefit for pension settlement costs in 2014, $0.7 million, net of $0.4 million tax benefit, for 2013 and $0.6 million, net of $0.3 million tax benefit in 2012. (See Note 8)