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, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Total	$ 1,188,673	$ 1,112,314	$ 1,005,574
United States Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash & Cash Equivalents	770	775
Equity securities	451,893	484,822
Fixed income securities	405,162	338,193
Total	857,825	823,790
U K Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash & Cash Equivalents	935	12,418
Equity securities	67,224	146,575
Fixed income securities	234,775	113,250
Other investments	25,868	13,915
Total	328,802	286,158
Quoted Prices in Active Markets for Identical Assets Level (1) [Member] | United States Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash & Cash Equivalents	770	775
Equity securities	153,129	187,685
Fixed income securities	137,693	123,776
Total	291,592	312,236
Quoted Prices in Active Markets for Identical Assets Level (1) [Member] | U K Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash & Cash Equivalents	935	12,418
Equity securities	67,224	146,575
Fixed income securities	234,775	113,250
Total	302,934	272,243
Significant Other Observable Inputs Level (2) [Member] | United States Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity securities	298,764	297,137
Fixed income securities	267,469	214,417
Total	566,233	511,554
Significant Other Observable Inputs Level (2) [Member] | U K Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	12,775
Total	12,775
Significant Unobservable Inputs Level (3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	13,093	13,915	13,822
Significant Unobservable Inputs Level (3) [Member] | U K Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other investments	13,093	13,915
Total	$ 13,093	$ 13,915