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Fair Value of Financial Instruments (Details) - USD ($)	12 Months Ended
Fair Value of Financial Instruments (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Oct. 02, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	$ 16,687,000	$ 12,586,000
Derivative liabilities	0	265,000
Non-real estate investment	2,713,000
Gross unrealized gain	806,000
Gross unrealized losses	0
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Non-real estate investment	146,880,000	0
Due in 1 year	6,175,000
Due in 1 year through 5 years	140,705,000
Total	146,880,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Non-real estate investment	147,686,000	0
Due in 1 year	6,187,000
Due in 1 year through 5 years	141,499,000
Total	147,686,000
Unsecured Debt \| Registered Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt instrument, face amount			$ 400,000,000.0
Discount net of amortization	648,000	722,000
Unsecured Debt \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	2,274,352,000	1,974,278,000
Unsecured Debt \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	2,227,265,000	1,960,560,000
Secured Debt \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	365,381,000	464,311,000
Secured Debt \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	354,109,000	458,441,000
In-Substance Defeased Debt \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	138,223,000	0
In-Substance Defeased Debt \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	135,894,000	0
Joint venture partner debt \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	66,136,000	0
Joint venture partner debt \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Notes payable	66,136,000	0
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	0	0
Derivative liabilities	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	16,687,000	12,586,000
Derivative liabilities	0	265,000
Level 2 \| Non-Real Estate Investmentest
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Non-real estate investment	2,713,000
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Derivative assets	0	0
Derivative liabilities	$ 0	$ 0