Sale of Common Stock (Details) - Common Stock - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended
Aug. 31, 2018	Jun. 30, 2018	Sep. 30, 2018
Class of Stock [Line Items]
Aggregate offering price			$ 75,000,000.0
Commission rate (percent)			3.00%
Stock issued (in shares)	6,000,000	740,417
Proceeds from stock issuance	$ 292,900,000	$ 30,300,000
Underwriting discounts and commissions and other offering expenses	$ 19,100,000	$ 1,100,000

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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