Shareholder's Equity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders Equity Note [Line Items]
Common stock, shares outstanding	113,844,267	113,643,166
Common shares and operating partnership units outstanding	117,955,568	117,834,752
Preferred Stock, Liquidation Preference, Value	$ 43,400,000
Preferred Stock, Liquidation Preference Per Share	$ 50.00
Preferred Stock, Redemption Date	Oct. 01, 2026
Preferred Stock, Redemption Price Per Share	$ 50.00
Preferred Stock, Dividend Rate, Percentage	8.50%
Preferred Stock, Dividend Rate, Per-Dollar-Amount	$ 4.25
Dividend And Distribution Reinvestment And Share Purchase Plan
Stockholders Equity Note [Line Items]
Common stock issued for shareholders to reinvest distributions (shares)	9,721	9,568	7,906
Dividend And Distribution Reinvestment And Share Purchase Plan | Minimum
Stockholders Equity Note [Line Items]
Optional cash investments in common shares	$ 250
Dividend And Distribution Reinvestment And Share Purchase Plan | Maximum
Stockholders Equity Note [Line Items]
Optional cash investments in common shares	$ 5,000
Common stock registered for Dividend and Distribution Reinvestment and Share Purchase Plan (shares)	1,940,500
Discount rate on sale of common stock (percent)	5.00%
Parent Company [Member]
Stockholders Equity Note [Line Items]
Preferred Stock, Shares Outstanding	867,846	867,846
Common stock, shares outstanding	113,844,267	113,643,166
Noncontrolling Interest in Joint Ventures	$ 2,306,000	$ 2,306,000	$ 2,306,000
Common stock registered for Dividend and Distribution Reinvestment and Share Purchase Plan (shares)	145,000,000	145,000,000
Proceeds from Issuance of Common Stock	$ 585,000	$ 1,557,000	291,000
Proceeds from Stock Options Exercised	$ 916,000	$ 432,000	0
Preferred Stock, Liquidation Preference Per Share	$ 50	$ 50
Employee Stock Option [Member]
Stockholders Equity Note [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	90,615	108,438
Proceeds from Stock Options Exercised	$ 900,000	$ 400,000	$ 0
Noncontrolling Interest
Stockholders Equity Note [Line Items]
Common Shares Issuable Upon Conversion Of Convertible Stock	4,111,301	4,191,586
Limited Partners' Capital Account	$ 393,500,000	$ 421,500,000
Redeemable Capital Shares Par Or Stated Value Per Share	$ 95.70	$ 100.56