Earnings Per Share - Calculations of Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	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, 2019	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share And Equity [Abstract]
Net income	$ 12,243	$ 3,007	$ 13,249	$ 19,081	$ 19,394	$ (11,135)	$ 2,372	$ 22,624	$ 5,482	$ 15,432	$ 5,304	$ 6,610	$ 47,580	$ 33,255	$ 32,828
Basic weighted average common shares outstanding													34,764	24,826	23,201
Add: Incremental shares for:
Dilutive effect of warrants														116	93
Dilutive effect of restricted stock													300	315	76
Diluted weighted average common shares outstanding													35,064	25,257	23,370
Net income per common share
Basic	$ 0.35	$ 0.09	$ 0.38	$ 0.55	$ 0.66	$ (0.48)	$ 0.10	$ 0.97	$ 0.24	$ 0.67	$ 0.23	$ 0.28	$ 1.37	$ 1.34	$ 1.41
Diluted	$ 0.35	$ 0.09	$ 0.38	$ 0.54	$ 0.65	$ (0.48)	$ 0.10	$ 0.96	$ 0.24	$ 0.66	$ 0.23	$ 0.28	$ 1.36	$ 1.32	$ 1.40