Quarterly Financial Data (Unaudited) - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2014
Quarterly Financial Data [Abstract]
Total revenue	$ 113,680	$ 119,217	$ 119,151	$ 120,296	$ 114,186	$ 111,299	$ 107,790	$ 107,126	$ 472,344	$ 440,401	$ 391,453
Gross profit	101,949	107,197	107,263	107,324	101,565	98,990	95,525	94,745	423,733	390,825	338,765
Income from operations	48,972	50,681	56,299	55,429	46,906	41,731	46,521	44,634	211,381	179,792	129,724
Net income	$ 33,326	$ 33,171	$ 36,683	$ 36,771	$ 30,806	$ 28,170	$ 30,464	$ 28,967	$ 139,951	$ 118,407	$ 85,783
Net income per common share:
Basic (in dollars per share)	$ 0.41	$ 0.40	$ 0.44	$ 0.44	$ 0.36	$ 0.32	$ 0.34	$ 0.32	$ 1.69	$ 1.34	$ 0.93
Diluted (in dollars per share)	$ 0.41	$ 0.40	$ 0.44	$ 0.44	$ 0.36	$ 0.32	$ 0.34	$ 0.32	$ 1.68	$ 1.33	$ 0.92
Weighted average shares outstanding:
Basic (in shares)	81,282	83,081	83,315	83,876	85,056	87,355	89,942	91,183	82,892	88,398	92,648
Diluted (in shares)	81,599	83,373	83,703	84,320	85,585	87,853	90,471	91,891	83,309	89,016	93,665