Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income attributable to common stockholders—basic	$ 20,052	$ 5,554	$ 21,669	$ 4,482
Net income attributable to nonvested restricted stockholders	24	7	25	5
Net income	$ 20,076	$ 5,561	$ 21,694	$ 4,487
Weighted average common shares outstanding - basic (in shares)	16,584,106	16,313,312	16,573,545	16,291,324
Shares issuable under stock options (in shares)	122,897	139,187	122,142	135,513
Weighted average common shares outstanding—diluted (in shares)	16,707,003	16,452,499	16,695,687	16,426,837
Net income (loss) per common share - basic (in US$ per share)	$ 1.21	$ 0.34	$ 1.31	$ 0.28
Net income (loss) per common share - diluted (in US$ per share)	$ 1.20	$ 0.34	$ 1.30	$ 0.27