Shareholders' Equity - Share Awards (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) installment shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 shares
2009 Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	172,700	145,800	136,600
Number of installments | installment	5
Unvested shares (in shares)	231,301	182,224	157,521	106,680
2023 (in shares)	84,941
2024 (in shares)	67,620
2025 (in shares)	50,500
2026 (in shares)	28,240
Estimated future compensation expense for the unvested shares | $	$ 4,343
Weighted average period of recognition of compensation expenses (in years)	22 months
Compensation expense | $	$ 2,905	$ 2,868	$ 3,315
Shares available for issuance under plan (in shares)	847,631
Officers and Other Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of shares, net (in shares)	141,200	117,800	108,600
Issuance of shares, net | $	$ 2,470	$ 2,994	$ 2,502
Trustees | 2009 Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	3,500	3,500	3,500
Aggregate market value of shares awarded | $	$ 593	$ 837	$ 745
Market value of common shares awarded to each trustee (in dollars) | $	$ 66	$ 105	$ 93