Recent Accounting Standards - Line Items Adjusted in Consolidated Statement of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenues		$ 122,152	$ 126,010	$ 365,721	$ 367,462
Sales and marketing expenses		45,429	42,005	147,742	123,213
Provision for income taxes		(1,240)	2,536	(699)	9,463
Net income		$ 12,699	$ 18,184	$ 19,200	$ 43,694
Diluted earnings per share	[1]	$ 1.10	$ 1.58	$ 1.67	$ 3.78
Product licenses
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenues		$ 20,264	$ 22,356	$ 56,857	$ 62,730
Product support
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenues		$ 74,463	72,881	$ 222,554	214,159
As Reported | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Sales and marketing expenses			41,806		122,635
Provision for income taxes			2,197		8,804
Net income			$ 17,924		$ 43,867
Diluted earnings per share			$ 1.56		$ 3.79
As Reported | Product licenses | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenues			$ 21,553		$ 61,683
As Reported | Product support | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenues			72,886		214,142
Effect of the Adoption | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Sales and marketing expenses			199		578
Provision for income taxes			339		659
Net income			$ 260		$ (173)
Diluted earnings per share			$ 0.02		$ (0.01)
Effect of the Adoption | Product licenses | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenues			$ 803		$ 1,047
Effect of the Adoption | Product support | ASU 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenues			$ (5)		$ 17

[1] Basic and fully diluted earnings per share for class A and class B common stock are the same.