Notes and Bonds Payable - Senior and Term Notes (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020	Oct. 02, 2020	Mar. 18, 2020	May 31, 2019	Dec. 11, 2017	Apr. 24, 2015	Feb. 28, 2014
Debt Instrument [Line Items]
Debt issuance costs	$ (9,245,000)
Notes and bonds payable	1,801,325,000	$ 1,602,769,000
Medium-term Notes | Term Loan due 2024
Debt Instrument [Line Items]
Senior and term notes face value	200,000,000	200,000,000			$ 200,000,000			$ 200,000,000
Debt issuance costs	(540,000)	(764,000)			$ (400,000)
Notes and bonds payable	$ 199,460,000	199,236,000
Medium-term Notes | Term Loan due 2026
Debt Instrument [Line Items]
Effective Interest rate	248.00%
Senior and term notes face value	$ 150,000,000	150,000,000
Debt issuance costs	(624,000)	(521,000)
Notes and bonds payable	149,376,000	149,479,000
Senior Notes | Senior Notes due 2025
Debt Instrument [Line Items]
Effective Interest rate							4.08%
Senior and term notes face value	250,000,000	250,000,000					$ 250,000,000
Unaccreted discount	(78,000)	(100,000)					$ (200,000)
Debt issuance costs	(882,000)	(1,124,000)
Notes and bonds payable	249,040,000	248,776,000
Senior Notes | Senior Notes due 2028
Debt Instrument [Line Items]
Effective Interest rate						3.84%
Senior and term notes face value	300,000,000	300,000,000				$ 300,000,000
Unaccreted discount	(1,637,000)	(1,872,000)				$ (2,500,000)
Debt issuance costs	(1,751,000)	(2,005,000)
Notes and bonds payable	296,612,000	296,123,000
Senior Notes | Senior Notes due 2030
Debt Instrument [Line Items]
Effective Interest rate				2.71%
Senior and term notes face value	300,000,000	300,000,000		$ 300,000,000
Unaccreted discount	(844,000)	(935,000)		$ (1,000,000)
Debt issuance costs	(2,343,000)	(2,597,000)
Notes and bonds payable	296,813,000	296,468,000
Senior Notes | Senior Notes due 2031
Debt Instrument [Line Items]
Effective Interest rate			2.24%
Senior and term notes face value	300,000,000	300,000,000	$ 300,000,000
Unaccreted discount	(2,171,000)	(2,382,000)	$ (2,400,000)
Debt issuance costs	(2,455,000)	(2,694,000)
Notes and bonds payable	$ 295,374,000	$ 294,924,000