Summary of Significant Accounting Policies - Summary of Impacts of Adopting ASC 606 on Condensed Statement of Income (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues									$ 875,059	$ 789,582	$ 760,958
Cost of revenues:
Total cost of revenues	$ 130,180	$ 109,052	$ 109,492	$ 101,096	$ 99,726	$ 99,717	$ 97,660	$ 97,708	449,820	394,811	375,147
Other expenses									338,252
Income before income taxes	25,567	20,492	20,724	20,204	21,671	23,386	20,303	22,350	86,987	87,710	99,999
Income tax provision	$ (4,669)	$ (4,391)	$ (5,607)	$ (6,190)	$ (6,705)	$ (8,806)	$ (8,722)	$ (2,113)	(20,857)	(26,346)	(37,117)
Net income									$ 66,130	$ 61,364	$ 62,882
Net income per diluted share	$ 0.64	$ 0.49	$ 0.46	$ 0.42	$ 0.45	$ 0.44	$ 0.35	$ 0.62	$ 2.01	$ 1.87	$ 1.90
Adjustments | ASC 606
Revenues:
Total revenues									$ 1,264
Cost of revenues:
Total cost of revenues									(944)
Income before income taxes									2,208
Income tax provision									(640)
Net income									$ 1,568
Net income per diluted share									$ 0.05
Balances without Adoption of ASC 606 | ASC 606
Revenues:
Total revenues									$ 876,323
Cost of revenues:
Total cost of revenues									448,876
Other expenses									338,252
Income before income taxes									89,195
Income tax provision									(21,497)
Net income									$ 67,698
Net income per diluted share									$ 2.06
Cloud and Related Services
Revenues:
Total revenues									$ 766,377	$ 651,010	$ 606,936
Cost of revenues:
Total cost of revenues									392,801	315,006	282,952
Cloud and Related Services | Adjustments | ASC 606
Revenues:
Total revenues									(25,960)
Cost of revenues:
Total cost of revenues									(20,419)
Cloud and Related Services | Balances without Adoption of ASC 606 | ASC 606
Revenues:
Total revenues									740,417
Cost of revenues:
Total cost of revenues									372,382
Software and Services
Revenues:
Total revenues									58,101	62,892	79,400
Cost of revenues:
Total cost of revenues									34,870	39,018	49,202
Software and Services | Adjustments | ASC 606
Revenues:
Total revenues									6,072
Cost of revenues:
Total cost of revenues									875
Software and Services | Balances without Adoption of ASC 606 | ASC 606
Revenues:
Total revenues									64,173
Cost of revenues:
Total cost of revenues									35,745
Maintenance
Revenues:
Total revenues									50,581	75,680	74,622
Cost of revenues:
Total cost of revenues									22,149	$ 40,787	$ 42,993
Maintenance | Adjustments | ASC 606
Revenues:
Total revenues									21,152
Cost of revenues:
Total cost of revenues									18,600
Maintenance | Balances without Adoption of ASC 606 | ASC 606
Revenues:
Total revenues									71,733
Cost of revenues:
Total cost of revenues									$ 40,749