Pensions and Other Postretirement Benefits - Summary of Pension Plan Assets Measured at Fair Value on Recurring Basis by Fair Value Hierarchy (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	$ 445,299	$ 434,569
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	288,018	307,914
Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	114,364	84,294
Pooled Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	22,623	22,430
Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	15,069	13,512
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	5,225	6,419
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	279,828	350,302
Fair Value, Inputs, Level 1 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	233,156	307,486
Fair Value, Inputs, Level 1 | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	41,447	36,749
Fair Value, Inputs, Level 1 | Pooled Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Inputs, Level 1 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	5,225	6,067
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	149,649	69,975
Fair Value, Inputs, Level 2 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	54,614	0
Fair Value, Inputs, Level 2 | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	72,412	47,545
Fair Value, Inputs, Level 2 | Pooled Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	22,623	22,430
Fair Value, Inputs, Level 2 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Inputs, Level 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	15,822	14,292
Fair Value, Inputs, Level 3 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	248	428
Fair Value, Inputs, Level 3 | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	505	0
Fair Value, Inputs, Level 3 | Pooled Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	0	0
Fair Value, Inputs, Level 3 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	15,069	13,512	12,254
Fair Value, Inputs, Level 3 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets measured at fair value	$ 0	$ 352