Notes Payable (Details)		1 Months Ended	3 Months Ended
	Mar. 20, 2020 USD ($)	Mar. 31, 2020 USD ($) instrument	Mar. 31, 2020 USD ($) instrument	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($) instrument	Sep. 30, 2017 USD ($) instrument	Dec. 31, 2016 USD ($) instrument	Oct. 31, 2015 USD ($) instrument	May 31, 2014 USD ($) instrument	Apr. 30, 2013 USD ($) instrument
Debt Instrument [Line Items]
Loss deferred in other comprehensive income			$ 7,617,000	$ 0
Proceeds from notes payable			692,646,000	0
Payment of debt issuance costs			6,397,000	40,000
Payment of make-whole premium			$ 16,679,000	$ 0
Forward Swap
Debt Instrument [Line Items]
Number of interest rate derivatives terminated | instrument		3	3		2	2	2	4	3	4
Aggregate notional amount		$ 200,000,000	$ 200,000,000		$ 250,000,000	$ 250,000,000	$ 180,000,000	$ 300,000,000	$ 225,000,000	$ 240,000,000
Loss deferred in other comprehensive income		13,141,000
2030 Notes | Loans Payable
Debt Instrument [Line Items]
Principal amount		$ 400,000,000	$ 400,000,000
Stated interest rate		2.50%	2.50%
Aggregate purchase price		$ 398,712,000	$ 398,712,000
Discount		$ 1,288,000	$ 1,288,000
Effective Rate		2.536%	2.536%
Proceeds from notes payable		$ 395,062,000
Payment of debt issuance costs		3,650,000
2050 Notes | Loans Payable
Debt Instrument [Line Items]
Principal amount		$ 300,000,000	$ 300,000,000
Stated interest rate		3.10%	3.10%
Aggregate purchase price		$ 293,934,000	$ 293,934,000
Discount		$ 6,066,000	$ 6,066,000
Effective Rate		3.205%	3.205%
Proceeds from notes payable		$ 290,459,000
Payment of debt issuance costs		$ 3,475,000
2022 Notes | Loans Payable
Debt Instrument [Line Items]
Stated interest rate	3.80%
Notes payable redeemed	$ 325,000,000
Redemption price, percent of principal amount	100.00%
Payment of make-whole premium	$ 16,679,000