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Stock Awards - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 11.1 $ 9.2 $ 8.8
Stock-based compensation expense, unrecognized cost $ 12.8    
Stock-based compensation expense, unrecognized cost, reorganization period (in years) 2 years 3 months 18 days    
Restricted equity awards, fair value $ 10.2 $ 10.2 $ 9.2
Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance award vesting period in years 10 years    
Equity Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Reserved shares of common stock for awards under the Equity Incentive Plan 8,196,770    
Common stock remaining for future stock awards transferred to the equity incentive plan 5,605,272    
Maximum number of shares of common stock that may be awarded 5,000,000    
Service-Based Awards [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years) 5 years    
Service-Based Awards [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years) 3 years    
40% Of 2015 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years) 3 years    
Share based payment award, expected volatility rate 40.00%    
Stock-based awards expiration date Dec. 31, 2017    
Share based payment award, weighted average risk-free rate of return 1.10%    
Common stock options awarded, dividend yield 7.20%    
Percentage of performance award grant in period 20.00%    
Percentage of shareholder return annually 9.00%    
Annual total shareholder return (in years) 3 years    
30% of 2015 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years) 5 years    
Share based payment award, expected volatility rate 27.00%    
Share based payment award, weighted average risk-free rate of return 1.10%    
Common stock options awarded, dividend yield 7.20%    
Percentage of performance award grant in period 30.00%    
Percentage of performance award to be earned of shareholder return reaches shareholder limit 100.00%    
30% of 2015 Performance Awards [Member] | If Any Shares Are Earned From This Award [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation award vesting rights Vest in equal annual amounts on December 31, 2017, 2018 and 2019.    
30% of 2015 Performance Awards [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of shareholder return to be earned 35.00%    
30% of 2015 Performance Awards [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of shareholder return to be earned 20.00%    
Remaining % of 2015 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years) 5 years    
Share based payment award, expected volatility rate 20.00%    
Share based payment award, weighted average risk-free rate of return 1.10%    
Common stock options awarded, dividend yield 7.20%    
Percentage of performance award to be earned of shareholder return reaches shareholder limit 100.00%    
Percentage of shareholder return to be earned 6.00%    
Remaining % of 2015 Performance Awards [Member] | If Any Shares Are Earned From This Award [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation award vesting rights Vest in equal annual amounts on December 31, 2017, 2018 and 2019.    
2015 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of performance awards forfeited 4,500    
Number of performance awards earned and vested 0    
Number of performance awards to be earned 867,388    
40% of 2014 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years)   3 years  
Share based payment award, expected volatility rate   40.00%  
Stock-based awards expiration date   Dec. 31, 2018  
Share based payment award, weighted average risk-free rate of return   1.70%  
Common stock options awarded, dividend yield   8.00%  
Percentage of performance award grant in period   27.00%  
Percentage of shareholder return annually   9.00%  
Annual total shareholder return (in years)   5 years  
30% of 2014 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years)   5 years  
Share based payment award, expected volatility rate   27.00%  
Share based payment award, weighted average risk-free rate of return   0.80%  
Common stock options awarded, dividend yield   8.00%  
Percentage of performance award grant in period   30.00%  
Percentage of performance award to be earned of shareholder return reaches shareholder limit   100.00%  
30% of 2014 Performance Awards [Member] | If Any Shares Are Earned From This Award [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation award vesting rights Vest in equal annual amounts on December 31, 2016, 2017 and 2018.    
30% of 2014 Performance Awards [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of shareholder return to be earned   35.00%  
30% of 2014 Performance Awards [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of shareholder return to be earned   27.00%  
Remaining % of 2014 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years)   5 years  
Share based payment award, expected volatility rate   27.00%  
Share based payment award, weighted average risk-free rate of return   0.80%  
Common stock options awarded, dividend yield   8.00%  
Percentage of performance award to be earned of shareholder return reaches shareholder limit   100.00%  
Percentage of shareholder return to be earned   6.00%  
Remaining % of 2014 Performance Awards [Member] | If Any Shares Are Earned From This Award [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation award vesting rights Vest in equal annual amounts on December 31, 2016, 2017 and 2018    
2014 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of performance awards earned and vested   108,261  
Number of performance awards to be earned   771,897  
27% of 2013 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance award vesting period in years     2 years
Share-based compensation arrangement by share based payment award, expected service period (in years)     3 years
Share based payment award, expected volatility rate     27.00%
Stock-based awards expiration date     Dec. 31, 2017
Share based payment award, weighted average risk-free rate of return     0.72%
Common stock options awarded, dividend yield     8.00%
Percentage of performance award grant in period     27.00%
Percentage of shareholder return annually     8.50%
Annual total shareholder return (in years)     5 years
Number of shares sold under performance awards     0
36% of 2013 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years)     5 years
Share based payment award, expected volatility rate     28.00%
Share based payment award, weighted average risk-free rate of return     0.38%
Common stock options awarded, dividend yield     8.00%
Percentage of performance award grant in period     36.00%
Percentage of performance award to be earned of shareholder return reaches shareholder limit     100.00%
36% of 2013 Performance Awards [Member] | If Any Shares Are Earned From This Award [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation award vesting rights Vest in equal annual amounts on December 31, 2015, 2016 and 2017    
36% of 2013 Performance Awards [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of shareholder return to be earned     33.50%
36% of 2013 Performance Awards [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of shareholder return to be earned     25.50%
Remaining % of 2013 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share based payment award, expected service period (in years)     5 years
Share based payment award, expected volatility rate     28.00%
Share based payment award, weighted average risk-free rate of return     0.38%
Common stock options awarded, dividend yield     8.00%
Percentage of performance award to be earned of shareholder return reaches shareholder limit     100.00%
Percentage of shareholder return to be earned     6.00%
Remaining % of 2013 Performance Awards [Member] | If Any Shares Are Earned From This Award [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation award vesting rights Vest in equal annual amounts on December 31, 2015, 2016 and 2017    
2013 Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of performance awards earned and vested   80,293 68,086
Number of performance awards to be earned 74,187    
Number of performance awards forfeited 550,000    
Number of performance awards earned and vested 0