Debt, Convertible Note (Details)				3 Months Ended		4 Months Ended	9 Months Ended
	Apr. 18, 2018 USD ($)	Feb. 28, 2018 shares	Jun. 16, 2016 USD ($)	Sep. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Apr. 17, 2018 USD ($)	Sep. 30, 2018 USD ($) d $ / shares shares	Sep. 30, 2017 USD ($)
Convertible Debt [Abstract]
Debt issuance costs							$ 7,243,000	$ 0
Loss on extinguishment of debt							(7,220,000)	$ 0
Class A Common Stock [Member]
Convertible Debt [Abstract]
Shares issued (in shares) | shares		1,535,652
Convertible Note [Member]
Convertible Debt [Abstract]
Original principal amount			$ 210,000,000	$ 210,000,000			$ 210,000,000
Interest rate				4.75%			4.75%
Redemption price, percentage of principal amount redeemed							100.00%
Threshold percentage of stock price trigger							180.00%
Threshold trading days | d							20
Threshold final trading days | d							3
Threshold consecutive trading days | d							30
Principal amount increments that can be repurchased upon a change in control or termination of trading of common stock							$ 1,000
Principal amount increments that can be converted							$ 1,000
Holding period following issue date before notes can be converted							6 months
Initial conversion rate (in shares) | shares							21.5054
Initial conversion price (in dollars per share) | $ / shares				$ 46.50			$ 46.50
Proceeds from issuance of notes			210,000,000
Liability component of convertible notes			199,100,000
Equity component of convertible notes allocated to additional paid-in capital			$ 10,900,000
Effective interest rate				7.10%			7.10%
Debt issuance costs							$ 6,600,000
Additions to deferred financing cost							6,300,000
Adjustments to additional paid-in capital for debt issuance costs							300,000
Interest expense				$ 0			3,500,000
Contractual interest				0			3,000,000
Amortization of debt issuance costs and debt discount				$ 0			$ 500,000
Payment for principal and accrued interest	$ 213,400,000
Accrued interest						$ 3,400,000
Loss on extinguishment of debt					$ (7,220,000)