Notes Payable (Details)	1 Months Ended
	Sep. 30, 2017 USD ($) derivative
Debt Instrument [Line Items]
Number of interest rate derivatives held | derivative	2
Derivative, notional amount	$ 250,000,000
Derivative liability at fair value	7,690,000
Notes Payable Issues September 2017
Debt Instrument [Line Items]
Face amount	$ 400,000,000
Interest rate, stated percentage	3.50%
Notes payable net price at issuance	$ 398,372,000
Unamortized discount	$ 1,628,000
Interest rate, effective percentage	3.548%
Proceeds from Issuance of Senior Long-term Debt	$ 394,722,000
Debt costs	3,650,000
Other Comprehensive Income (Loss)
Debt Instrument [Line Items]
Derivative liability at fair value	$ 7,688,000