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Share-based compensation plans - Additional Information (Details) $ / shares in Units, $ in Thousands | 12 Months Ended | 48 Months Ended |
--- | --- | --- | ---
Dec. 31, 2021 USD ($) installment $ / shares shares | Dec. 31, 2020 USD ($) $ / shares shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2019 | Apr. 17, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Maximum number of shares of common stock issued (in shares) | shares |  |  |  |  | 12,000,000
Shares available for grant (in shares) | shares | 8,494,373 |  |  |  |
Compensation cost for share-based payment arrangements | $ 22,608 | $ 10,607 | $ 14,334 |  |
Related tax benefit recognized in net income | 5,715 | 2,686 | 3,500 |  |
Additional net excess tax benefit realized | 1,110 | 2,528 | 3,520 |  |
Noncash stock-based compensation associated performance contingent restricted stock units | 11,477 | 2,023 | 5,171 |  |
Compensation deferrals in current year | $ 2,507 | $ 2,593 | $ 2,585 |  |
Restricted Stock Units (RSUs) | Executive Officers and Key Management Employees |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Minimum vesting period | 3 years |  |  |  |
Restricted Stock Units (RSUs) | Executive Officers and Key Management Employees | Share-based Compensation Award, Tranche One |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting percentage | 33.33% |  |  |  |
Restricted Stock Units (RSUs) | Executive Officers and Key Management Employees | Share-based Compensation Award, Tranche Two |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting percentage | 33.33% |  |  |  |
Restricted Stock Units (RSUs) | Executive Officers and Key Management Employees | Share-based Compensation Award, Tranche Three |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting percentage | 33.33% |  |  |  |
Restricted Stock Units (RSUs) | Executives and Directors |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Minimum vesting period | 5 years |  |  |  |
Granted, weighted-average grant date fair value (usd per share) | $ / shares | $ 57.77 | $ 54.16 | $ 57.76 |  |
Fair value of vested units | $ 4,063 | $ 3,277 | $ 3,217 |  |
Restricted Stock Units (RSUs) | Executives and Directors | Share-based Compensation Award, Tranche Three |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting percentage | 33.33% |  |  |  |
Restricted Stock Units (RSUs) | Executives and Directors | Share-based Compensation Award, Tranche Four |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting percentage | 33.33% |  |  |  |
Restricted Stock Units (RSUs) | Executives and Directors | Share-based Compensation Award, Tranche Five |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting percentage | 33.33% |  |  |  |
Restricted Stock Awards |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Granted, weighted-average grant date fair value (usd per share) | $ / shares | $ 57.77 |  |  |  |
Vested units in period (in shares) | shares | 0 |  |  |  |
Restricted Stock Awards | Executives and Directors |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Noncash stock-based compensation associated performance contingent restricted stock units | $ 8,278 | $ 4,549 | $ 3,351 |  |
Total unrecognized compensation cost related to nonvested awards | $ 8,061 |  |  |  |
Weighted-average period | 46 months |  |  |  |
Performance Shares |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Granted, weighted-average grant date fair value (usd per share) | $ / shares | $ 55.95 | $ 52 | $ 56.04 |  |
Total unrecognized compensation cost related to nonvested awards | $ 14,259 |  |  |  |
Weighted-average period | 21 months |  |  |  |
Performance period | 3 years |  |  |  |
Number of common shares to be converted into for each share upon conversion | 1 |  |  |  |
Performance Shares | 2021 PCSU |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Performance period | 3 years |  |  |  |
Total performance contingent restricted stock units vested , minimum (in shares) | shares | 0 |  |  |  |
Total performance contingent restricted stock units, maximum (in shares) | shares | 285,724 |  |  |  |
Performance Shares | 2020 PCSU |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Performance period | 3 years |  |  |  |
Total performance contingent restricted stock units vested , minimum (in shares) | shares | 0 |  |  |  |
Total performance contingent restricted stock units, maximum (in shares) | shares | 297,648 |  |  |  |
Performance Shares | 2019 PCSU |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Fair value of vested units | $ 3,719 |  |  |  |
Total performance contingent restricted stock units, maximum (in shares) | shares | 64,243 |  |  |  |
Performance Shares | 2018 PCSU |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Fair value of vested units |  | $ 8,288 |  |  |
Vested units in period (in shares) | shares |  | 139,886 |  |  |
Performance Shares | 2017 PCSU |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Fair value of vested units |  |  | $ 5,217 |  |
Vested units in period (in shares) | shares |  |  | 84,522 |  |
Stock Appreciation Rights (SARs) |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting percentage | 33.33% |  |  |  |
Total unrecognized compensation cost related to nonvested awards | $ 40 |  |  |  |
Weighted-average period | 2 months |  |  |  |
Vested units in period (in shares) | shares | 0 |  |  |  |
Aggregate intrinsic value of options and SARs exercised | $ 2,575 | $ 2,771 | $ 11,836 |  |
Weighted-average fair value of awards granted (usd per share) | $ / shares |  |  | $ 8.3 |  |
Weighted average remaining contractual life for SAR's, outstanding | 6 years 1 month 6 days |  |  |  |
Weighted average remaining contractual life for SAR's, exercisable | 5 years 10 months 24 days |  |  |  |
Aggregate intrinsic value for SAR's, outstanding | $ 3,598 |  |  |  |
Aggregate intrinsic value for SAR's, exercisable | $ 2,800 |  |  |  |
Fair market value of the Company’s stock used to calculate intrinsic value (usd per share) | $ / shares | $ 57.89 |  |  |  |
Stock Appreciation Rights (SARs) | Granted 2015 through 2019 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Minimum vesting period |  |  |  | 3 years |
Term of award | 10 years |  |  |  |
Unvested award termination period upon change in control | 2 years |  |  |  |
Stock Options and Stock Appreciation Rights Sars |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Compensation cost for share-based payment arrangements | $ 347 | $ 1,442 | $ 3,227 |  |
Deferred Stock Equivalent Units | Non-employee directors | Share-based Compensation Award, Tranche One |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Number of annual distribution installments | installment | 1 |  |  |  |
Deferred Stock Equivalent Units | Non-employee directors | Share-based Compensation Award, Tranche Two |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Number of annual distribution installments | installment | 3 |  |  |  |
Deferred Stock Equivalent Units | Non-employee directors | Share-based Compensation Award, Tranche Three |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Number of annual distribution installments | installment | 5 |  |  |  |

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