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Stock Based Compensation - Additional Information (Detail) - USD ($) |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
May. 21, 2013 | Jan. 31, 2016 | Jul. 31, 2015 | Jan. 31, 2015 | Jul. 31, 2014 | Jan. 31, 2014 | Jul. 31, 2013 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Percentage of common stock price paid |  |  |  |  |  |  |  | 85.00% |  |  |
Stock options term |  |  |  |  |  |  |  | 7 years |  |  |
Restricted stock unit awards granted |  |  |  |  |  |  |  | 1,681,000 | 1,870,000 | 2,110,000 |
Weighted average grant date fair value of restricted stock units granted |  |  |  |  |  |  |  | $ 17.36 | $ 18.41 | $ 16.62 |
Stock options granted |  |  |  |  |  |  |  | 132,000 | 89,000 | 213,000 |
Weighted average grant date fair value |  |  |  |  |  |  |  | $ 4.43 | $ 5.49 | $ 6.09 |
Total unrecognized expense related to non-vested restricted stock unit awards and stock options |  |  |  |  |  |  |  | $ 44,900,000 |  |  |
Unrecognized expense related to non-vested restricted stock unit awards and stock options expected to be recognized over weighted average period, in years |  |  |  |  |  |  |  | 2 years 3 months 18 days |  |  |
Stock based compensation expense |  |  |  |  |  | $ 6,600,000 |  | $ 30,451,000 | $ 40,307,000 | $ 36,612,000 |
Maximum percent of shares allowed to purchase |  |  |  |  |  |  |  | 10.00% |  |  |
Fair market value |  |  |  |  |  |  |  | $ 25,000 |  |  |
Maximum number of shares allowed to purchase |  |  |  |  |  |  |  | 6,000 |  |  |
Common stock issued to employees |  |  | 500,000 | 500,000 | 500,000 | 400,000 | 400,000 |  |  |  |
Value of common stock issued to employees per share |  |  | $ 16.40 | $ 16.82 | $ 16.66 | $ 14.98 | $ 14.94 |  |  |  |
Number of shares available for grant |  |  |  |  |  |  |  | 10,914,000 | 12,443,000 | 14,213,000 | 6,414,000
Stock Options |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Percentage of common stock price paid |  |  |  |  |  |  |  | 100.00% |  |  |
Period of stock granted to employees and executive officers vest in equal annual installments |  |  |  |  |  |  |  | 4 years |  |  |
Restricted Stock Units |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Restricted stock unit awards granted |  |  |  |  |  |  |  | 1,681,000 | 1,870,000 | 2,110,000 |
Restricted Stock Units | Employees |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Period of stock granted to employees and executive officers vest in equal annual installments |  |  |  |  |  |  |  | 4 years |  |  |
Restricted Stock Units | Director |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Period of stock granted to employees and executive officers vest in equal annual installments |  |  |  |  |  |  |  | 1 year |  |  |
Percentage of awards vesting on the first anniversary of grant date |  |  |  |  |  |  |  | 100.00% |  |  |
TSR Performance-Based Restricted Stock Units |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Total shareholder return performance measurement period |  |  |  |  |  | 3 years |  |  |  |  |
Minimum age of retirement to be eligible for PRSUs |  |  |  |  |  | 60 years |  |  |  |  |
Minimum years of service for retirement to be eligible for PRSUs |  |  |  |  |  | 10 years |  |  |  |  |
Restricted stock unit awards granted |  |  |  |  |  |  |  | 200,000 | 100,000 |  |
Weighted average grant date fair value of restricted stock units granted |  |  |  |  |  |  |  | $ 18.21 | $ 22.06 |  |
Estimated annual dividend amount per share |  |  |  |  |  |  |  | 0.24 | 0.24 |  |
Stock price |  |  |  |  |  |  |  | $ 18.10 | $ 19.16 |  |
TSR Performance-Based Restricted Stock Units | Share-based Compensation Award, Tranche One |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Percentage of vesting of target shares upon performance achieved |  |  |  |  |  | 200.00% |  |  |  |  |
TSR Performance-Based Restricted Stock Units | Share-based Compensation Award, Tranche Two |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Percentage of vesting of target shares upon performance achieved |  |  |  |  |  | 0.00% |  |  |  |  |
Employee Stock Purchase Plan |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Number of shares available for grant |  |  |  |  |  |  |  | 4,900,000 |  |  |
2006 Equity and Cash Compensation Incentive Plan |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Employee Stock Purchase Plan to increase the number of shares issuable | 10,000,000 |  |  |  |  |  |  |  |  |  |
Aggregate number of shares issuable | 32,000,000 |  |  |  |  |  |  |  |  |  |
1996 Employee Stock Purchase Plan |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Employee Stock Purchase Plan to increase the number of shares issuable | 5,000,000 |  |  |  |  |  |  |  |  |  |
Aggregate number of shares issuable | 30,400,000 |  |  |  |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |
Common stock issued to employees |  | 500,000 |  |  |  |  |  |  |  |  |
Value of common stock issued to employees per share |  | $ 17.57 |  |  |  |  |  |  |  |  |

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