Postretirement Benefit Plans - Company's Asset Allocations for its U.S. Pension Plans by Asset Category (Detail) (United States [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Total	$ 126,369	$ 133,264	$ 124,682
Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	3,352	3,116
Commodities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	2,023	912
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	76,896	91,810
Level 1 [Member] | Commodities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	2,023	912
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	49,473	41,454
Level 2 [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	3,352	3,116
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,963	2,471
Cash and Cash Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	1,963	2,471
U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	34,885	32,567
U.S. Equities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	34,885	32,567
Non-U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	12,478	11,892
Non-U.S. Equities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	12,478	11,892
Employer Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	21,575	37,823
Employer Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	21,575	37,823
Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	68,938	82,282
Equities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	68,938	82,282
U.S. Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	27,676	24,733
U.S. Corporate Bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	27,676	24,733
U.S. Government and Agency Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	10,677	9,101
U.S. Government and Agency Bonds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	350	2,526
U.S. Government and Agency Bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	10,327	6,575
Other Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	6,155	4,559
Other Bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	6,155	4,559
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	47,860	41,509
Debt Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	350	2,526
Debt Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	47,510	38,983
Real Estate Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	5,585	6,090
Real Estate Fund [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	$ 5,585	$ 6,090