Shareholders' Equity - Narrative (Details)													1 Months Ended				12 Months Ended
	Nov. 30, 2020 USD ($)	Oct. 20, 2020 USD ($) $ / shares	Sep. 16, 2020 $ / shares	Mar. 10, 2020 USD ($)	Oct. 23, 2019 USD ($) $ / shares	Sep. 24, 2019 $ / shares	Mar. 13, 2019 USD ($)	Oct. 26, 2018 $ / shares	Oct. 23, 2018 USD ($)	Oct. 09, 2018 $ / shares	Mar. 14, 2018 USD ($)	Mar. 15, 2017 USD ($)	Feb. 29, 2020 USD ($)	Mar. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) $ / shares shares	Oct. 02, 2020	Mar. 31, 2020 USD ($)	Oct. 08, 2019	Oct. 07, 2019
Class of Stock [Line Items]
Repurchase of shares																	$ 20,869,000		$ 88,255,000
Distributions declared per common share (in dollars per share) | $ / shares			$ 3.50			$ 3.50				$ 2.50
Distributions paid per common share (in dollars per share) | $ / shares		$ 3.50			$ 3.50			$ 2.50
Cash distributions paid		$ 426,700,000			$ 427,700,000				$ 304,700,000				$ 2,900,000		$ 1,200,000		$ 427,795,000	$ 428,649,000	$ 304,612,000
Preferred shares, of beneficial interest, shares outstanding (in shares) | shares																	4,915,196	4,915,196
Preferred shares, dividend yield																	6.50%	6.50%
Common Shares
Class of Stock [Line Items]
Stock repurchase program, additional authorized amount (up to)											$ 150,000,000.0	$ 150,000,000.0
Stock repurchase program, period in force											12 months	12 months
Stock repurchase program, amount not utilized														$ 130,900,000		$ 81,000,000.0
Number of shares repurchased (in shares) | shares																		0	2,970,209
Stock repurchased and retired during period, price per share (in dollars per share) | $ / shares																			$ 29.67
Redemption of shares																			$ 88,100,000
Stock repurchase program, remaining authorized repurchase amount																	$ 150,000,000.0
Surrender of shares for tax withholding (in shares) | shares																	184,068	168,327	193,521
Common shares from conversion of preferred shares (in shares) | shares																	3,236,657
Common Shares | Share Repurchase Program, March 13, 2019
Class of Stock [Line Items]
Stock repurchase program, additional 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) | shares																	711,000
Average cost per share (in dollars per share) | $ / shares																	$ 29.31
Repurchase of shares																	$ 20,800,000
Common Shares | Share Repurchase Program, March 10, 2020
Class of Stock [Line Items]
Stock repurchase program, period in force				12 months
Stock repurchase program, authorized amount (up to)				$ 150,000,000.0
Common Shares | Share Repurchase Program, March 2017 Authorization
Class of Stock [Line Items]
Redemption of shares	$ 69,000,000.0
Common Shares | Share Repurchase Program, March 2018 Authorization
Class of Stock [Line Items]
Redemption of shares	$ 19,100,000
Series D Preferred Stock
Class of Stock [Line Items]
Preferred shares dividend (in dollars per share) | $ / shares																	$ 1.625
Initial conversion rate										0.480775										0.6585		0.5813	0.5215
Initial conversion price per share (in dollars per share) | $ / shares																	$ 37.97
Additional common shares (in shares) | shares																	3,236,657
Liquidation preference (in dollars per share) | $ / shares																	$ 25.00
Percentage of average closing market price of the entity's common stock based on which ratio for conversion of preferred shares into common shares is determined																	98.00%
Purchase price as a percentage of liquidation preference																	100.00%
Common shares from conversion of preferred shares (in shares) | shares																	4,915,196