Share-Based Compensation - Additional Information (Detail) | 3 Months Ended | | |
Mar. 31, 2018USD ($)Deferralshares | Mar. 31, 2017USD ($)shares | Dec. 31, 2017shares | May 10, 2016shares |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Deferred shares and held by the rabbi trust | 289,138 | | 289,026 | |
1999 Stock Option Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Exercised, Number of Shares | 0 | | | |
Granted, Number of Shares | 0 | | | |
Long Term Incentive Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Common shares reserved for awards | 900,000 | | | |
2016 Incentive Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Common shares reserved for awards | | | | 1,000,000 |
Incentive plan expiry date | May 10, 2026 | | | |
Long Term Incentive Plan Stock Option [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Exercised, Number of Shares | 0 | 0 | | |
Weighted-average period | 1 year 8 months 12 days | | | |
Granted, Number of Shares | 0 | 0 | | |
Long Term Incentive Plan Stock Option [Member] | Maximum [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Compensation expenses | $ | $ 100,000 | $ 100,000 | | |
Expected compensation cost related to unvested awards not yet recognized | $ | $ 100,000 | | | |
Long Term Incentive Plan Stock Option [Member] | After One Year [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Stock option awards vesting percentage | 50.00% | | | |
Long Term Incentive Plan Stock Option [Member] | After Two Years [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Stock option awards vesting percentage | 75.00% | | | |
Long Term Incentive Plan Stock Option [Member] | After Three Years [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Stock option awards vesting percentage | 100.00% | | | |
Deferred Compensation Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Number of deferrals | Deferral | 2 | | | |
Stock Options [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Exercised, Number of Shares | 0 | 0 | | |
Stock Options [Member] | 1999 Stock Option Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Compensation expenses | $ | $ 0 | $ 0 | | |
Stock Options [Member] | 2016 Incentive Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Common shares reserved for awards | | | | 100,000 |
Restricted Stock Units (RSUs) [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Common shares reserved for awards | 800,000 | | | |
Restricted Stock Units (RSUs) [Member] | 2016 Incentive Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Common shares reserved for awards | | | | 900,000 |
Long Term Incentive Stock Option [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Common shares reserved for awards | 100,000 | | | |
Long Term Incentive Stock Option [Member] | Minimum [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Option issued under plan vest and expire | 5 years | | | |
Long Term Incentive Stock Option [Member] | Maximum [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Option issued under plan vest and expire | 10 years | | | |
Time-Based RSUs [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Compensation expenses | $ | $ 100,000 | 100,000 | | |
Compensation cost expected to be recognized over period | $ | $ 1,000,000 | | | |
Weighted-average period | 2 years 3 months 18 days | | | |
Performance-Based RSUs [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | | | | |
Weighted-average period | 2 years 1 month 6 days | | | |
Performance-based compensation expense (income) | $ | $ 700,000 | $ 400,000 | | |
Remaining compensation expense | $ | $ 5,400,000 | | | |