Income Taxes - Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Current expense									$ 328	$ 338
Deferred expense									5,502	1,776
Total expense	$ 747	$ 738	$ 627	$ 3,719	$ 769	$ 539	$ 605	$ 201	$ 5,830	$ 2,114