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Shareholders' capital - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands |  |  |  |  | 1 Months Ended | 12 Months Ended |  |  |  |  |
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Mar. 31, 2024 $ / shares | Feb. 19, 2020 $ / shares shares | Dec. 20, 2018 USD ($) $ / shares shares | Dec. 20, 2018 CAD ($) shares | Apr. 24, 2018 USD ($) $ / shares shares | Apr. 24, 2018 CAD ($) shares | Oct. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2019 USD ($) Right vote $ / shares shares | Dec. 31, 2019 USD ($) $ / shares $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) $ / shares $ / shares shares | Dec. 31, 2019 CAD ($) $ / shares shares | Feb. 28, 2019 USD ($) | Dec. 31, 2018 $ / shares | Dec. 20, 2018 $ / shares | Apr. 24, 2018 $ / shares
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of entitled votes per common share | vote |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |
Number of voting rights per share | Right |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |
Discount rate on share purchases |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |
Discount rate on share purchases under dividend reinvestment plan |  |  |  |  |  |  |  | 5.00% |  |  |  |  |  |  |  |
Dividend reinvestment plan shares issued (in shares) |  |  |  |  |  |  |  | 1,244,696 |  |  |  |  |  |  |  |
Carrying amount C$ |  |  |  |  |  |  |  | $ 184,299,000 | $ 184,299,000 | $ 184,299,000 | $ 184,299,000 |  |  |  |  |
Preferred stock redemption price per share (in CAD per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  | $ 25 |  |  |  |
Total share-based compensation expense | $ |  |  |  |  |  |  |  | $ 10,553,000 |  | $ 9,458,000 |  |  |  |  |  |
Options exercised (in shares) |  |  |  |  |  |  |  | 3,882,505 |  | 1,589,211 |  |  |  |  |  |
Options exercised (CAD per share) | $ / shares |  |  |  |  |  |  |  |  | $ 11.23 |  | $ 10.66 |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of outstanding stock to be purchased to acquire discount (or more) |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |
Employee Stock Option |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total share-based compensation expense | $ |  |  |  |  |  |  |  | $ 1,288,000 |  | $ 2,054,000 |  |  |  |  |  |
Unrecognized compensation costs, non-vested options | $ |  |  |  |  |  |  |  | $ 1,252,000 | $ 1,252,000 |  |  |  |  |  |  |
Unrecognized compensation costs, non-vested options, period of recognition |  |  |  |  |  |  |  | 1 year 8 months 4 days |  |  |  |  |  |  |  |
Stock Option Plans | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of shares reserves under plan (must not exceed) |  |  |  |  |  |  |  | 8.00% |  |  |  |  |  |  |  |
Performance Share Units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum aggregate number of shares reserved for future issuance (in shares) |  |  |  |  |  |  |  | 7,000,000 | 7,000,000 |  |  | 7,000,000 |  |  |  |
Performance share units granting period |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |
Percentage of shares issued on number of PSU grants, minimum |  |  |  |  |  |  |  | 2.00% |  |  |  |  |  |  |  |
Percentage of shares issued on number of PSU grants, maximum |  |  |  |  |  |  |  | 237.00% |  |  |  |  |  |  |  |
Employee share purchase |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total share-based compensation expense | $ |  |  |  |  |  |  |  | $ 322,000 |  | $ 312,000 |  |  |  |  |  |
Vesting period of matching contribution shares |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |
Maximum aggregate number of shares reserved for future issuance (in shares) |  |  |  |  |  |  |  | 2,000,000 | 2,000,000 |  |  | 2,000,000 |  |  |  |
Common stock, shares issued (in shares) |  |  |  |  |  |  |  | 253,538 | 253,538 | 252,698 | 252,698 | 253,538 |  |  |  |
Deferred Share Units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum aggregate number of shares reserved for future issuance (in shares) |  |  |  |  |  |  |  | 1,000,000 | 1,000,000 |  |  | 1,000,000 |  |  |  |
Shares issued during period (in shares) |  |  |  |  |  |  |  | 460,418 |  | 380,656 |  |  |  |  |  |
Performance and restricted share units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total share-based compensation expense | $ |  |  |  |  |  |  |  | $ 8,145,000 |  | $ 6,378,000 |  |  |  |  |  |
Unrecognized compensation costs, non-vested awards | $ |  |  |  |  |  |  |  | $ 12,750,000 | $ 12,750,000 |  |  |  |  |  |  |
Unrecognized compensation costs, non-vested options, period of recognition |  |  |  |  |  |  |  | 1 year 10 months 9 days |  |  |  |  |  |  |  |
Series A Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock issued (in shares) |  |  |  |  |  |  |  | 4,800,000 | 4,800,000 | 4,800,000 | 4,800,000 | 4,800,000 |  |  |  |
Shares issued, price per share (CAD per share) | (per share) |  |  |  |  |  |  |  |  |  | $ 25 | $ 25 | $ 25 |  |  |  |
Carrying amount C$ |  |  |  |  |  |  |  | $ 100,463,000 | $ 100,463,000 | $ 100,463,000 | $ 100,463,000 | $ 116,546 |  |  |  |
Fixed cumulative annual dividend per share (CAD per share) | (per share) |  |  |  |  |  |  |  | $ 1.2905 | $ 1.2905 |  |  |  |  | $ 1.125 |  |
Subsequent yield period |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |
Preferred stock, Subsequent redemption period |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |
Series C Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock redemption price per share (in CAD per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  | $ 53,400 |  |  |  |
Redeemable preferred stock issued (in shares) |  |  |  |  |  |  |  | 100 | 100 |  |  | 100 |  |  |  |
Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock issued (in shares) |  |  |  |  |  |  |  | 4,000,000 | 4,000,000 | 4,000,000 | 4,000,000 | 4,000,000 |  |  |  |
Shares issued, price per share (CAD per share) | (per share) |  |  |  |  |  |  |  |  |  | $ 25 | $ 25 | $ 25 |  |  |  |
Carrying amount C$ |  |  |  |  |  |  |  | $ 83,836,000 | $ 83,836,000 | $ 83,836,000 | $ 83,836,000 | $ 97,259 |  |  |  |
Fixed cumulative annual dividend per share (CAD per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  | $ 1.25 |  |  |  |
Preferred stock, Subsequent redemption period |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |
Government of Canada Bond Yield | Series A Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividend variable interest rate |  |  |  |  |  |  |  | 2.94% |  |  |  |  |  |  |  |
Range One | Employee share purchase |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employer matching contribution, percent |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |
Range Two | Employee share purchase |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employer matching contribution, percent |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |
Public Stock Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, price per share | (per share) |  |  | $ 10.09 |  | $ 9.23 |  | $ 13.50 |  |  |  |  |  |  |  | $ 13.76 | $ 11.85
Issuance cost |  |  | $ 366,000 | $ 492 | $ 590,000 | $ 765 | $ 14,418,000 |  |  |  |  |  |  |  |  |
Public Stock Offering | Common shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares issued pursuant to public offering |  |  | 12,536,350 | 12,536,350 | 37,505,274 | 37,505,274 | 26,252,542 |  |  |  |  |  |  |  |  |
Cash proceeds from issuance of shares |  |  | $ 126,485,000 | $ 172,500 | $ 346,458,000 | $ 444,437 | $ 354,409,000 |  |  |  |  |  |  |  |  |
ATM Equity Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares issued pursuant to public offering |  |  |  |  |  |  |  | 1,756,799 |  |  |  |  |  |  |  |
Cash proceeds from issuance of shares | $ |  |  |  |  |  |  |  | $ 21,704,000 |  |  |  |  |  |  |  |
Sale of stock, program costs | $ |  |  |  |  |  |  |  | 2,122,000 |  |  |  |  |  |  |  |
Sale Of Stock, Consideration Received On Transaction, Gross | $ |  |  |  |  |  |  |  | $ 22,034,000 |  |  |  |  |  |  |  |
Sale of Stock, Value of Shares Issued in Transaction | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ 250,000 |  |  |
Shares issued, price per share (CAD per share) | $ / shares |  |  |  |  |  |  |  | $ 12.54 | $ 12.54 |  |  |  |  |  |  |
Forecast | Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed cumulative annual dividend per share (CAD per share) | $ / shares | $ 1.2728 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock redemption price per share (in CAD per share) | $ / shares | $ 25 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forecast | Government of Canada Bond Yield | Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 3.28% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options exercised (in shares) |  | 394,939 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options exercised (CAD per share) | $ / shares |  | $ 12.77 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | Common shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options settled at cash value for payment of the exercise price and for tax withholdings (in shares) |  | 279,422 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | Treasury Stock, Common |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued from treasury for option exercise (in shares) |  | 115,517 |  |  |  |  |  |  |  |  |  |  |  |  |  |

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