Postretirement Benefits - Analysis of Impact on Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Compensation And Retirement Disclosure [Abstract]
Balance at January 1	$ (168,129)	$ (119,863)	$ (105,903)
Amortization of Prior service cost	2,276	2,146	2,080
Amortization of Net actuarial (gain) loss	16,090	12,653	10,071
Amortization of Transition obligation	0	0	(5)
Total amortization	18,366	14,799	12,146
Plan amendments	0	(3,452)	0
Experience gain (loss)	52,296	(59,613)	(26,106)
Balance at December 31	$ (97,467)	$ (168,129)	$ (119,863)