Notes Payable (Details)	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) instrument	Sep. 30, 2019 instrument	Sep. 30, 2018 USD ($) instrument	Dec. 31, 2017 instrument	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Oct. 31, 2015 USD ($) instrument	May 31, 2014 USD ($) instrument
Debt Instrument [Line Items]
Loss deferred in other comprehensive income		$ 0	$ 0	$ 0	$ 7,617,000
Proceeds from notes payable				441,594,000	692,646,000
Payment of debt issuance costs				12,743,000	7,809,000
Make-whole premium		$ 0	$ 0	$ 21,328,000	$ 16,679,000
Forward Swap
Debt Instrument [Line Items]
Number of interest rate derivatives terminated | instrument						3	2	2	2			4	3
Aggregate notional amount						$ 200,000,000		$ 250,000,000		$ 250,000,000	$ 180,000,000	$ 300,000,000	$ 225,000,000
2030 Notes | Loans Payable
Debt Instrument [Line Items]
Principal amount	$ 450,000,000
Stated interest rate	3.50%
Aggregate purchase price	$ 441,594,000
Discount	$ 8,406,000
Effective Rate	3.602%
Proceeds from notes payable	$ 436,417,000
Payment of debt issuance costs	$ 5,177,000
2022 Notes | Loans Payable
Debt Instrument [Line Items]
Stated interest rate	3.30%
Notes payable redeemed	$ 350,000,000
Redemption price, percent of principal amount	100.00%
Make-whole premium	$ 21,328,000