Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
U.S. corporate income tax rate	35.00%	21.00%
Blended corporate tax rate		24.50%
Decrease in tax provision due to revaluation of net deferred tax liability		$ (43,429)
Unrecognized tax Benefits that would impact effective tax rate		1,016	$ 284
State
Income Taxes [Line Items]
Net operating losses		$ 83,996
Net operating losses, expiration start year		2019
Net operating losses, expiration end year		2038