Pension and Postretirement Benefits - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Amortization of prior service benefit	$ (146)
Net periodic benefit (credit) cost	10	19	114
Pension Plan and SERP Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	0	0	282
Interest cost	19,073	17,860	19,888
Curtailment gain	0	0	(780)
Expected return on plan assets	(33,942)	(30,480)	(28,899)
Amortization of prior service benefit	0	0	(133)
Amortization of net actuarial loss	763	5,078	3,646
Net periodic benefit (credit) cost	(14,106)	(7,542)	(5,996)
Amortization of actuarial loss reclassified from accumulated other comprehensive losses	(354)	(1,320)	(279)
Amortization of prior service benefit reclassified from accumulated other comprehensive losses	0	0	133
Prior service benefit	0	0	(7,475)
Net loss recognized reclassified from accumulated other comprehensive losses	(409)	(3,758)	(3,368)
Actuarial gain (loss)	59,272	(70,065)	26,184
Total recognized in other comprehensive loss (income)	58,509	(75,143)	15,195
Total recognized in net periodic benefit (credit) cost and other comprehensive loss (income)	44,403	(82,685)	9,199
Postretirement Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	0	0	0
Interest cost	593	608	779
Curtailment gain	0	0	0
Expected return on plan assets	(786)	(919)	(255)
Amortization of prior service benefit	(146)	(146)	(146)
Amortization of net actuarial loss	517	767	634
Net periodic benefit (credit) cost	178	310	1,012
Amortization of actuarial loss reclassified from accumulated other comprehensive losses	0	0	0
Amortization of prior service benefit reclassified from accumulated other comprehensive losses	146	146	146
Prior service benefit	0	0	0
Net loss recognized reclassified from accumulated other comprehensive losses	0	0	0
Actuarial gain (loss)	(886)	(77)	1,742
Total recognized in other comprehensive loss (income)	(740)	69	1,888
Total recognized in net periodic benefit (credit) cost and other comprehensive loss (income)	$ (562)	$ 379	$ 2,900