Pension and Postretirement Benefits - Total Investments Plans Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 532,403	$ 593,927
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	421,987	471,704
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	85,077	110,267
Cash and Accrued Items [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,339	11,956
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	170,528	186,312
Level 1 [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60,128	64,575
Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	85,065	109,781
Level 1 [Member] | Cash and Accrued Items [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,335	11,956
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	356,123	402,602
Level 2 [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	356,107	402,116
Level 2 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12	486
Level 2 [Member] | Cash and Accrued Items [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,752	5,013
Level 3 [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 5,752	$ 5,013	$ 3,769