Notes Payable (Details)	1 Months Ended
	Sep. 30, 2018 USD ($) derivative
Notes Payable Due October 2028
Debt Instrument [Line Items]
Principal	$ 400,000,000
Stated Rate	4.30%
Purchase price	$ 397,152,000
Unamortized discount	2,848,000
Proceeds from debt issuance, net of issuance costs	393,502,000
Debt costs	3,650,000
Notes Payable Due October 2048
Debt Instrument [Line Items]
Principal	$ 300,000,000
Stated Rate	4.80%
Purchase price	$ 295,761,000
Unamortized discount	$ 4,239,000
Effective interest rate	4.89%
Proceeds from debt issuance, net of issuance costs	$ 292,386,000
Debt costs	3,375,000
2021 Notes
Debt Instrument [Line Items]
Principal	$ 300,000,000
Stated Rate	5.50%
Debt instrument, redemption price, percentage	100.00%
Debt repayment, make whole amount	$ 18,240,000
Interest Rate Swap | Notes Payable Due October 2028
Debt Instrument [Line Items]
Effective interest rate	4.388%
Number of derivative financial instruments outstanding | derivative	2
Notional amount	$ 250,000,000
Liability amount from termination of hedge agreement	$ 4,080,000