Quarterly Financial Data (Unaudited) - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015
Total revenue	$ 123,682	$ 119,277	$ 119,933	$ 120,050	$ 113,680	$ 119,217	$ 119,151	$ 120,296	$ 482,942	$ 472,344	$ 440,401
Gross profit	111,568	107,010	108,354	108,544	101,949	107,197	107,263	107,324	435,476	423,733	390,825
Income from operations	48,948	52,273	56,065	54,730	48,972	50,681	56,299	55,429	212,016	211,381	179,792
Net income	$ 54,352	$ 35,834	$ 37,010	$ 35,000	$ 33,326	$ 33,171	$ 36,683	$ 36,771	$ 162,196	$ 139,951	$ 118,407
Net income per common share:
Basic (in dollars per share)	$ 0.73	$ 0.47	$ 0.48	$ 0.44	$ 0.41	$ 0.40	$ 0.44	$ 0.44	$ 2.12	$ 1.69	$ 1.34
Diluted (in dollars per share)	$ 0.73	$ 0.47	$ 0.48	$ 0.44	$ 0.41	$ 0.40	$ 0.44	$ 0.44	$ 2.11	$ 1.68	$ 1.33
Weighted average shares outstanding:
Basic (in shares)	74,294	75,676	76,905	79,048	81,282	83,081	83,315	83,876	76,491	82,892	88,398
Diluted (in shares)	74,830	76,182	77,318	79,385	81,599	83,373	83,703	84,320	76,978	83,309	89,016