Shareholders' Equity (Details) $ / shares in Units, $ in Thousands									3 Months Ended
	Jul. 16, 2020 USD ($) $ / shares	Jun. 30, 2020 $ / shares shares	May 28, 2020 employee $ / shares shares	May 21, 2020 USD ($) $ / shares	Mar. 13, 2020 $ / shares shares	Feb. 21, 2020 employee $ / shares shares	Feb. 20, 2020 USD ($) $ / shares	Jan. 09, 2020 $ / shares shares	Jun. 30, 2020 USD ($) $ / shares	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)
Shareholders' Equity
Dividends paid (in dollars per share)				$ 0.33			$ 0.33
Dividends paid | $				$ 21,511			$ 21,510		$ 21,511	$ 21,510	$ 21,475	$ 21,474
Common shares
Shareholders' Equity
Number of Shares (in shares) | shares		613			531			420
Price per Share (in dollars per share)		$ 20.55			$ 17.75			$ 22.01	$ 20.55
Trustees
Shareholders' Equity
Number of officers elected | employee						2
Number of officers | employee			7
Trustees | Common shares
Shareholders' Equity
Common shares granted (in shares) | shares						3,000
Per share value of common shares granted (in dollars per share)			$ 18.77			$ 23.54
Shares granted in period (in shares) | shares			3,500
Subsequent Event
Shareholders' Equity
Dividends paid (in dollars per share)	$ 0.33
Dividends paid | $	$ 21,500