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Employer Share Plans - Schedule of Share-Based Compensation Awards (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Compensation and Retirement Disclosure [Abstract]    
Stock options $ 841us-gaap_StockOptionPlanExpense $ 649us-gaap_StockOptionPlanExpense
Restricted stock awards 781us-gaap_RestrictedStockExpense 741us-gaap_RestrictedStockExpense
Total stock-based compensation expense $ 1,622us-gaap_AllocatedShareBasedCompensationExpense $ 1,390us-gaap_AllocatedShareBasedCompensationExpense