Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Current:
Federal			$ (26)	$ 1,092	$ 11,120
State and foreign			9,470	6,359	3,193
Total			9,444	7,451	14,313
Deferred:
Federal			9,076	5,190	(3,766)
State and foreign			(371)	(1,435)	(1,186)
Total			8,705	3,755	(4,952)
Total income tax expense			18,149	$ 11,206	$ 9,361
Charge resulting from remeasured deferred tax asset	$ 1,900	$ 2,800	2,100
Charge resulting from recording valuation allowance not likely to be utilized			$ 2,600