Shareholders' Equity - Narrative (Details) - USD ($)					1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 20, 2020	Sep. 16, 2020	Mar. 10, 2020	Mar. 13, 2019	Feb. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020
Class of Stock [Line Items]
Repurchase of shares								$ 20,869,000
Distributions declared per common share/unit (in dollars per share)		$ 3.50				$ 3.50	$ 3.50	$ 3.50	$ 3.50
Distributions to common shareholders/unitholders					$ 2,900,000			$ 1,936,000	$ 1,160,000
Subsequent event
Class of Stock [Line Items]
Distributions to common shareholders/unitholders	$ 426,700,000
Common Shares
Class of Stock [Line Items]
Surrender of shares for tax withholding (in shares)								183,992	168,327
Share Repurchase Program, March 13, 2019 | Common Shares
Class of Stock [Line Items]
Stock repurchase program, authorized amount (up to)				$ 150,000,000.0
Stock repurchase program, period in force				12 months
Stock repurchase program, amount expired										$ 129,200,000
Repurchase of shares (in shares)								711,000
Average cost per share (in dollars per share)								$ 29.31
Repurchase of shares								$ 20,800,000
Share Repurchase Program, March 10, 2020 | Common Shares
Class of Stock [Line Items]
Stock repurchase program, authorized amount (up to)			$ 150,000,000.0
Stock repurchase program, period in force			12 months