Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Income Taxes [Line Items]
U.S. corporate income tax rate	21.00%				35.00%
Decrease in tax provision due to revaluation of net deferred tax liability		$ (40,515)
Blended corporate tax rate				24.50%
Decrease in effective tax rate	3.50%
Effective tax rate excluding revaluation of deferred taxes		34.30%
Scenario, Forecast
Income Taxes [Line Items]
U.S. corporate income tax rate			21.00%