Pensions and Postretirement Benefits Other than Pensions - Assets of U.S and U.K Plans Using Fair Value Hierarchy (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	$ 1,005,574	$ 907,131	$ 928,323
United States plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents	18,487	16,106
Equity securities	431,383	412,809
Fixed income securities	296,001	251,302
Total	745,871	680,217
United Kingdom plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents	2,231	796
Equity securities	152,434	126,126
Fixed income securities	72,251	66,491
Other investments	30,482	31,213
Total	257,398	224,626
Quoted Prices in Active Markets for Identical Assets Level (1) [Member] | United States plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents	18,487	16,106
Equity securities	147,397	168,240
Fixed income securities	97,974	83,274
Total	263,858	267,620
Quoted Prices in Active Markets for Identical Assets Level (1) [Member] | United Kingdom plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents	2,231	796
Equity securities	152,434	126,126
Fixed income securities	72,251	66,491
Other investments	16,660	18,379
Total	243,576	211,792
Significant Other Observable Inputs Level 2 [Member] | United States plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents
Equity securities	283,986	244,569
Fixed income securities	198,027	168,028
Total	482,013	412,597
Significant Other Observable Inputs Level 2 [Member] | United Kingdom plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents
Equity securities
Fixed income securities
Other investments
Total
Significant Unobservable Inputs Level 3 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Other investments	13,822	12,834	10,814
Significant Unobservable Inputs Level 3 [Member] | United States plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents
Equity securities
Fixed income securities
Total
Significant Unobservable Inputs Level 3 [Member] | United Kingdom plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Cash & Cash Equivalents
Equity securities
Fixed income securities
Other investments	13,822	12,834
Total	$ 13,822	$ 12,834