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Postretirement Benefit Plans - Defined Benefit Plans - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Feb. 18, 2015
Feb. 19, 2014
Defined Benefit Plan Disclosure [Line Items]          
Assets gains or losses added for prior year 80.00%        
Assets gains or losses added for second preceding year 60.00%        
Assets gains or losses added for third preceding year 40.00%        
Assets gains or losses added for fourth preceding year 20.00%        
Commodities [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 2.00%        
Expected long-term rate of return on assets 6.30%        
U.S Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of fixed income assets in debt securities 20.00%        
Common shares sold to the Company's ESOP trust       39,360 37,999
Expected payment related to qualified plan $ 0        
Expected payment related to unqualified plan $ 198,000        
U.K Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of premium estimated return for equities and properties to risk free rate 3.00%        
Percentage of long term return in cash 4.00%        
Expected payment related to qualified plan $ 361,000        
Equities [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 34.00%        
Expected long-term rate of return on assets 8.57%        
Equities [Member] | U.K Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 58.00%        
Debt Securities [Member] | U.S Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 35.00%        
Debt Securities [Member] | U.K Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 27.00%        
Real Estate Fund [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 4.00%        
Expected long-term rate of return on assets 7.30%        
Real Estate Fund [Member] | U.K Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 2.00%        
Employer Securities [Member] | U.S Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 25.00%        
Insurance Contracts [Member] | U.K Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 9.00%        
Cash [Member] | U.K Plans [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Percentage of target allocation for investment category 4.00%        
U.S. and international equities [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Expected long-term rate of return on assets 4.26%        
United States [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Accumulated benefit obligation at end of year $ 160,789,000        
Expected long-term rate of return on assets 7.50% 7.75% 7.75%    
United Kingdom [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Accumulated benefit obligation at end of year $ 19,950,000        
Expected long-term rate of return on assets 4.66% 5.84% 5.25%