Quarterly Financial Data (Unaudited) - (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2019	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Cash and cash equivalents	$ 71,926				$ 96,165				$ 71,926	$ 96,165
Accounts Receivable, Net, Current	47,784				21,910				47,784	21,910
Current contract assets	294,193				0				294,193	0
Prepaid expenses and other current assets	12,628								12,628
Prepaid income taxes	2,509								2,509
Assets, Current	429,040								429,040
Property, equipment and leasehold improvements, net	7,234				9,806				7,234	9,806
Computer software development costs, net	1,306								1,306
Goodwill	78,383								78,383
Intangible assets, net	33,607				35,310				33,607	35,310
Non-current contract assets	325,510				0				325,510	0
Contract costs	24,982				0				24,982	0
Non-current deferred tax assets	1,669				11,090				1,669	11,090
Other non-current assets	1,334								1,334
Assets	903,065				264,924				903,065	264,924
Accounts payable	5,891								5,891
Accrued expenses and other current liabilities	54,594				39,515				54,594	39,515
Income taxes payable	14,952								14,952
Borrowings under credit agreement	220,000								220,000
Current deferred revenue	25,318				286,845				25,318	286,845
Liabilities, Current	320,755								320,755
Non-current deferred revenue	19,573				28,259				19,573	28,259
Deferred income taxes	159,071				0				159,071	0
Other non-current liabilities	10,381				18,492				10,381	18,492
Commitments and contingencies (Note 16)
Series D redeemable convertible preferred stock, $0.10 par value—Authorized—3,636 shares as of June 30, 2019 and 2018 Issued and outstanding—none as of June 30, 2019 and 2018	0								0
Common stock, $0.10 par value—Authorized—210,000,000 shares Issued—103,642,292 shares at June 30, 2019 and 103,130,300 shares at June 30, 2018 Outstanding—68,624,566 shares at June 30, 2019 and 71,186,701 shares at June 30, 2018	10,365								10,365
Additional paid-in capital	739,099								739,099
Retained earnings	1,259,984				305,208				1,259,984	305,208
Accumulated other comprehensive income	336								336
Treasury Stock, Value	(1,616,499)								(1,616,499)
Stockholders' Equity Attributable to Parent	393,285								393,285			$ (75,034)
Total liabilities and stockholders' equity	903,065				264,924				903,065	264,924
Total revenue	195,769	$ 147,984	$ 140,423	$ 114,169
Gross profit	180,279	133,624	125,684	100,942					540,529	448,870	$ 435,476
Income from operations	111,223	70,831	63,758	36,990					282,802	209,641	212,016
Net income	$ 103,865	$ 61,587	$ 59,217	$ 38,066					$ 262,734	$ 148,688	$ 162,196
Net income per common share:
Basic (in dollars per share)	$ 1.51	$ 0.89	$ 0.84	$ 0.54					$ 3.76	$ 2.06	$ 2.12
Diluted (in dollars per share)	$ 1.49	$ 0.88	$ 0.83	$ 0.53					$ 3.71	$ 2.04	$ 2.11
Weighted average shares outstanding:
Basic (in shares)	68,839	69,423	70,428	70,988					69,925	72,140	76,491
Diluted (in shares)	69,638	70,160	71,148	72,015					70,787	72,956	76,978
Accounting Standards Update 2014-09 (Topic 606) [Member]
Cash and cash equivalents		$ 65,592	$ 54,428	$ 52,048	96,165					$ 96,165	$ 101,954	318,336
Accounts Receivable, Net, Current		41,640	52,933	50,346	41,810					41,810
Current contract assets		270,732	265,686	238,495	237,537					237,537
Current contract costs		0	0	0	0					0
Prepaid expenses and other current assets		11,124	10,330	12,992	10,509					10,509
Prepaid income taxes		1,573	921	1,422	2,601					2,601
Assets, Current		390,661	384,298	355,303	388,622					388,622
Property, equipment and leasehold improvements, net		7,589	8,311	9,006	9,806					9,806
Computer software development costs, net		1,452	691	695	646					646
Goodwill		73,534	74,802	75,649	75,590					75,590
Intangible assets, net		31,756	32,889	34,192	35,310					35,310
Non-current contract assets		318,752	338,060	353,449	319,840					319,840
Contract costs		24,325	23,046	21,296	20,500					20,500
Non-current deferred tax assets		1,696	1,651	1,176	1,232					1,232
Other non-current assets		1,279	1,075	1,279	1,297					1,297
Assets		851,044	864,823	852,045	852,843					852,843
Accounts payable		4,023	5,249	2,501	4,230					4,230
Accrued expenses and other current liabilities		42,746	36,688	32,000	39,515					39,515
Income taxes payable		35,582	43,573	46,869	1,698					1,698
Borrowings under credit agreement		220,000	220,000	170,000	170,000					170,000
Current deferred revenue		24,415	23,145	23,737	15,150					15,150
Liabilities, Current		326,766	328,655	275,107	230,593					230,593
Non-current deferred revenue		19,312	18,167	15,046	12,354					12,354
Deferred income taxes		135,535	137,872	140,197	184,901					184,901
Other non-current liabilities		12,403	16,192	16,833	17,068					17,068
Commitments and contingencies (Note 16)
Series D redeemable convertible preferred stock, $0.10 par value—Authorized—3,636 shares as of June 30, 2019 and 2018 Issued and outstanding—none as of June 30, 2019 and 2018		0	0	0	0					0
Common stock, $0.10 par value—Authorized—210,000,000 shares Issued—103,642,292 shares at June 30, 2019 and 103,130,300 shares at June 30, 2018 Outstanding—68,624,566 shares at June 30, 2019 and 71,186,701 shares at June 30, 2018		10,348	10,340	10,328	10,313					10,313
Additional paid-in capital		730,830	725,493	724,752	715,475					715,475
Retained earnings		1,156,120	1,094,533	1,035,316	997,250					997,250
Accumulated other comprehensive income		1,229	70	965	1,388					1,388
Treasury Stock, Value		(1,541,499)	(1,466,499)	(1,366,499)	(1,316,499)					(1,316,499)
Stockholders' Equity Attributable to Parent		357,028	363,937	404,862	407,927					407,927	286,243	$ 454,803
Total liabilities and stockholders' equity		851,044	864,823	852,045	852,843					852,843
Total revenue					159,084	$ 127,759	$ 105,529	$ 126,487
Gross profit					146,037	114,983	93,440	113,755		468,215	446,961
Income from operations					79,784	53,620	30,104	55,714		219,221	216,719
Net income					$ 76,646	$ 44,506	$ 132,030	$ 40,521		$ 293,703	$ 179,386
Net income per common share:
Basic (in dollars per share)					$ 1.07	$ 0.62	$ 1.83	$ 0.55		$ 4.07	$ 2.35
Diluted (in dollars per share)					$ 1.06	$ 0.61	$ 1.81	$ 0.55		$ 4.03	$ 2.33
Weighted average shares outstanding:
Basic (in shares)					71,349	71,828	72,342	73,024		72,140	76,491
Diluted (in shares)					72,315	72,663	73,036	73,609		72,956	76,978
Previously Reported [Member] | Accounting Standards Update 2014-09 (Topic 606) [Member]
Cash and cash equivalents		65,592	54,428	52,048	$ 96,165					$ 96,165
Accounts Receivable, Net, Current		45,293	56,586	53,999	41,810					41,810
Current contract assets		314,745	321,135	317,967	304,378					304,378
Current contract costs		24,325	23,046	21,296	20,500					20,500
Prepaid expenses and other current assets		11,124	10,330	12,992	10,509					10,509
Prepaid income taxes		1,573	921	1,422	2,601					2,601
Assets, Current		462,652	466,446	459,724	475,963					475,963
Property, equipment and leasehold improvements, net		7,589	8,311	9,006	9,806					9,806
Computer software development costs, net		1,452	691	695	646					646
Goodwill		73,534	74,802	75,649	75,590					75,590
Intangible assets, net		31,756	32,889	34,192	35,310					35,310
Non-current contract assets		358,709	366,581	357,947	340,622					340,622
Contract costs		0	0	0	0					0
Non-current deferred tax assets		1,696	1,651	1,176	11,090					11,090
Other non-current assets		1,279	1,075	1,279	1,297					1,297
Assets		938,667	952,446	939,668	950,324					950,324
Accounts payable		4,023	5,249	2,501	4,230					4,230
Accrued expenses and other current liabilities		42,746	36,688	32,000	39,515					39,515
Income taxes payable		35,582	43,573	46,869	1,698					1,698
Borrowings under credit agreement		220,000	220,000	170,000	170,000					170,000
Current deferred revenue		24,415	23,145	23,737	15,150					15,150
Liabilities, Current		326,766	328,655	275,107	230,593					230,593
Non-current deferred revenue		19,312	18,167	15,046	12,354					12,354
Deferred income taxes		154,901	157,238	159,563	214,125					214,125
Other non-current liabilities		12,403	16,192	16,833	17,068					17,068
Series D redeemable convertible preferred stock, $0.10 par value—Authorized—3,636 shares as of June 30, 2019 and 2018 Issued and outstanding—none as of June 30, 2019 and 2018		0	0	0	0					0
Common stock, $0.10 par value—Authorized—210,000,000 shares Issued—103,642,292 shares at June 30, 2019 and 103,130,300 shares at June 30, 2018 Outstanding—68,624,566 shares at June 30, 2019 and 71,186,701 shares at June 30, 2018		10,348	10,340	10,328	10,313					10,313
Additional paid-in capital		730,830	725,493	724,752	715,475					715,475
Retained earnings		1,224,377	1,162,790	1,103,573	1,065,507					1,065,507
Accumulated other comprehensive income		1,229	70	965	1,388					1,388
Treasury Stock, Value		(1,541,499)	(1,466,499)	(1,366,499)	(1,316,499)					(1,316,499)
Stockholders' Equity Attributable to Parent		425,285	432,194	473,119	476,184					476,184
Total liabilities and stockholders' equity		938,667	952,446	939,668	950,324					950,324
Restatement Adjustment [Member]
Accounts Receivable, Net, Current				3,700
Deferred income taxes				19,400	19,400					19,400
Retained earnings				68,300	68,300					68,300
Restatement Adjustment [Member] | Accounting Standards Update 2014-09 (Topic 606) [Member]
Cash and cash equivalents		0	0	0	0					0
Accounts Receivable, Net, Current		(3,653)	(3,653)	(3,653)	0					0
Current contract assets		(44,013)	(55,449)	(79,472)	(66,841)					(66,841)
Current contract costs		(24,325)	(23,046)	(21,296)	(20,500)					(20,500)
Prepaid expenses and other current assets		0	0	0	0					0
Prepaid income taxes		0	0	0	0					0
Assets, Current		(71,991)	(82,148)	(104,421)	(87,341)					(87,341)
Property, equipment and leasehold improvements, net		0	0	0	0					0
Computer software development costs, net		0	0	0	0					0
Goodwill		0	0	0	0					0
Intangible assets, net		0	0	0	0					0
Non-current contract assets		(39,957)	(28,521)	(4,498)	(20,782)					(20,782)
Contract costs		24,325	23,046	21,296	20,500					20,500
Non-current deferred tax assets		0	0	0	(9,858)					(9,858)
Other non-current assets		0	0	0	0					0
Assets		(87,623)	(87,623)	(87,623)	(97,481)					(97,481)
Accounts payable		0	0	0	0					0
Accrued expenses and other current liabilities		0	0	0	0					0
Income taxes payable		0	0	0	0					0
Borrowings under credit agreement		0	0	0	0					0
Current deferred revenue		0	0	0	0					0
Liabilities, Current		0	0	0	0					0
Non-current deferred revenue		0	0	0	0					0
Deferred income taxes		(19,366)	(19,366)	(19,366)	(29,224)					(29,224)
Other non-current liabilities		0	0	0	0					0
Series D redeemable convertible preferred stock, $0.10 par value—Authorized—3,636 shares as of June 30, 2019 and 2018 Issued and outstanding—none as of June 30, 2019 and 2018		0	0	0	0					0
Common stock, $0.10 par value—Authorized—210,000,000 shares Issued—103,642,292 shares at June 30, 2019 and 103,130,300 shares at June 30, 2018 Outstanding—68,624,566 shares at June 30, 2019 and 71,186,701 shares at June 30, 2018		0	0	0	0					0
Additional paid-in capital		0	0	0	0					0
Retained earnings		(68,257)	(68,257)	(68,257)	(68,257)					(68,257)
Accumulated other comprehensive income		0	0	0	0					0
Treasury Stock, Value		0	0	0	0					0
Stockholders' Equity Attributable to Parent		(68,257)	(68,257)	(68,257)	(68,257)					(68,257)
Total liabilities and stockholders' equity		$ (87,623)	$ (87,623)	$ (87,623)	$ (97,481)					$ (97,481)