Summary of Performance- and Market- Based Awards Granted (Detail) - shares	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Market Based Share Awards | 2015 Market-Based Share Plan | Performance Period Ending July 2016, 2017 and 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Measure	Total Shareholder Return
Number of Shares Granted	25,000	25,000
Period Expensed Through	2018-07	2018-07
Market Based Share Awards | 2015 Market-Based Share Plan | Performance Period Ending December 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Measure	Total Shareholder Return
Number of Shares Granted	57,982	57,982
Period Expensed Through	2017-12	2017-12
Performance Shares | 2015 Performance Share Plan | Performance Period Ending December 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Measure	Adjusted EPS
Number of Shares Granted	135,289	135,289
Period Expensed Through	2017-12	2017-12
Performance Shares | 2015 Performance Share Plan | Performance Period Ending December 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Measure	Revenues before Reimbursable Items and Adjusted EPS
Number of Shares Granted	165,543	165,543
Period Expensed Through	2017-12	2018-12
Performance Shares | 2014 Performance Shares | Performance Period Ending December 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Measure	Revenues before Reimbursable Items and Adjusted EPS
Number of Shares Granted	211,593	211,593
Period Expensed Through	2016-12	2016-12