Debt - Unsecured Term Loans (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jul. 31, 2019 USD ($)	Jul. 25, 2019 USD ($)	Jan. 07, 2019
Line Of Credit Facility Leverage Range [Line Items]
Number of term loans | loan	2
Outstanding principal balance	$ 1,019,569,000
Loss on early extinguishment of debt	$ 2,373,000	$ 0	$ 274,000
LIBOR | Unsecured Term Loan Due October 2023
Line Of Credit Facility Leverage Range [Line Items]
Interest rate at period end						2.41%
Less than or equal to 30% | LIBOR | $100 Million and $200 Million Term Loans
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.35%
Greater than 30% but less than or equal to 35% | LIBOR | $100 Million and $200 Million Term Loans
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.40%
Greater than 35% but less than or equal to 40% | LIBOR | $100 Million and $200 Million Term Loans
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.45%
Greater than 40% but less than or equal to 45% | LIBOR | $100 Million and $200 Million Term Loans
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.50%
Greater than 45% but less than or equal to 50% | LIBOR | $100 Million and $200 Million Term Loans
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.65%
Greater than 50% but less than or equal to 55% | LIBOR | $100 Million and $200 Million Term Loans
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.85%
Greater than 55% | LIBOR | $100 Million and $200 Million Term Loans
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	2.00%
Line Of Credit Facility Covenant Actual Results
Line Of Credit Facility Leverage Range [Line Items]
Maximum leverage ratio	0.285
Unsecured term loan
Line Of Credit Facility Leverage Range [Line Items]
Debt instrument, term (in years)	5 years
Accordion feature, higher borrowing capacity					$ 1,200,000,000
Unsecured term loan | Unsecured Term Loan Due July 2024
Line Of Credit Facility Leverage Range [Line Items]
Debt instrument, term (in years)	5 years
Outstanding principal balance	$ 350,000,000	0
Unsecured term loan | Unsecured Term Loan Due April 2022
Line Of Credit Facility Leverage Range [Line Items]
Number of term loans | loan	2
Outstanding principal balance	$ 0	200,000,000
Unsecured term loan | Unsecured Term Loan Due October 2023
Line Of Credit Facility Leverage Range [Line Items]
Outstanding principal balance	$ 50,000,000	50,000,000		$ 50,000,000
Unsecured term loan | Unsecured Term Loan, $175 million
Line Of Credit Facility Leverage Range [Line Items]
Outstanding principal balance					$ 175,000,000
Unsecured term loan | LIBOR
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.35%
Interest incurred on the facility	$ 13,700,000	$ 10,600,000	$ 6,200,000
Unsecured term loan | LIBOR | Unsecured Term Loan Due July 2024
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.40%
Unsecured term loan | LIBOR | Unsecured Term Loan Due April 2022
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.45%
Unsecured term loan | LIBOR | Unsecured Term Loan Due October 2023
Line Of Credit Facility Leverage Range [Line Items]
Basis spread on variable rate	1.40%
Unsecured term loan | Minimum | Greater than 30% but less than or equal to 35%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.30
Unsecured term loan | Minimum | Greater than 35% but less than or equal to 40%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.35
Unsecured term loan | Minimum | Greater than 40% but less than or equal to 45%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.4
Unsecured term loan | Minimum | Greater than 45% but less than or equal to 50%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.45
Unsecured term loan | Minimum | Greater than 50% but less than or equal to 55%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.5
Unsecured term loan | Minimum | Greater than 55%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.55
Unsecured term loan | Maximum | Less than or equal to 30%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.30
Unsecured term loan | Maximum | Greater than 30% but less than or equal to 35%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.35
Unsecured term loan | Maximum | Greater than 35% but less than or equal to 40%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.4
Unsecured term loan | Maximum | Greater than 40% but less than or equal to 45%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.45
Unsecured term loan | Maximum | Greater than 45% but less than or equal to 50%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.5
Unsecured term loan | Maximum | Greater than 50% but less than or equal to 55%
Line Of Credit Facility Leverage Range [Line Items]
Leverage Ratio	0.55