Summary of Impact of Adoption of ASU 606 (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Assets
Accounts receivable, unbilled receivables, and contract assets						$ 382,547
Long-term unbilled receivables	[1]	$ 169,330		$ 169,330		160,708
Deferred income taxes						14,240
Deferred contract costs						37,924
Other assets	[2]					416,148
Total assets	[1]	973,040		973,040		1,011,567
Liabilities and stockholders' equity
Deferred revenue	[1]	163,525		163,525		166,297
Long-term deferred revenue	[3]	6,210		6,210		3,706
Deferred income tax liabilities	[1]	38,208		38,208		38,463
Other liabilities	[4]					148,864
Total liabilities	[1]	333,868		333,868		357,330
Foreign currency translation adjustments						(6,460)
Retained earnings	[1]	506,769		506,769		508,051
Other equity	[5]					152,646
Total stockholders' equity	[1]	639,172		639,172		654,237
Total liabilities and stockholders' equity	[1]	973,040		973,040		1,011,567
Revenue:
Total revenue	[1]	196,779	$ 186,596	431,961	$ 442,905
Cost of revenue:
Total cost of revenue	[1]	73,817	67,875	149,431	135,965
Gross profit	[1]	122,962	118,721	282,530	306,940
Operating expenses:
Selling and marketing	[1]	93,972	75,200	182,355	144,881
Research and development	[1]	41,972	39,762	88,757	80,058
General and administrative	[1]	10,181	12,706	26,645	25,041
Total operating expenses	[1]	146,125	127,668	297,757	249,980
Income/(loss) from operations	[1]	(23,163)	(8,947)	(15,227)	56,960
Foreign currency transaction loss	[1]	1,244	(2,242)	159	(1,497)
Interest income, net	[1]	629	202	1,393	407
Other income, net	[1]		566	363	287
Income/(loss) before benefit from income taxes	[1]	(21,290)	(10,421)	(13,312)	56,157
Benefit from income taxes	[1]	(10,881)	(14,123)	(15,103)	(508)
Net income	[1]	$ (10,409)	$ 3,702	$ 1,791	$ 56,665
Earnings per share:
Basic	[1]	$ (0.13)	$ 0.05	$ 0.02	$ 0.74
Diluted	[1]	$ (0.13)	$ 0.04	$ 0.02	$ 0.69
Weighted-average number of common shares outstanding:
Basic	[1]	78,635	77,313	78,436	77,039
Diluted	[1]	78,635	82,945	83,247	82,412
Software license
Revenue:
Total revenue	[1]	$ 44,784	$ 51,150	$ 132,557	$ 178,158
Cost of revenue:
Total cost of revenue	[1]	1,262	1,250	2,517	2,550
Maintenance
Revenue:
Total revenue	[1]	65,906	59,424	130,431	118,137
Cost of revenue:
Total cost of revenue	[1]	5,874	7,011	11,956	14,229
Services
Revenue:
Total revenue	[1]	86,089	76,022	168,973	146,610
Cost of revenue:
Total cost of revenue	[1]	$ 66,681	59,614	$ 134,958	119,186
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09
Assets
Accounts receivable, unbilled receivables, and contract assets						248,331
Deferred income taxes						57,127
Other assets	[2]					416,148
Total assets						721,606
Liabilities and stockholders' equity
Deferred revenue						195,073
Long-term deferred revenue						6,591
Other liabilities	[4]					148,864
Total liabilities						350,528
Foreign currency translation adjustments						(3,494)
Retained earnings						221,926
Other equity	[5]					152,646
Total stockholders' equity						371,078
Total liabilities and stockholders' equity						721,606
Revenue:
Total revenue			197,980		421,227
Cost of revenue:
Total cost of revenue			67,875		135,965
Gross profit			130,105		285,262
Operating expenses:
Selling and marketing			75,887		147,175
Research and development			39,762		80,058
General and administrative			12,706		25,041
Total operating expenses			128,355		252,274
Income/(loss) from operations			1,750		32,988
Foreign currency transaction loss			(917)		(241)
Interest income, net			161		326
Other income, net			566		287
Income/(loss) before benefit from income taxes			1,560		33,360
Benefit from income taxes			(9,846)		(5,067)
Net income			$ 11,406		$ 38,427
Earnings per share:
Basic			$ 0.15		$ 0.50
Diluted			$ 0.14		$ 0.47
Weighted-average number of common shares outstanding:
Basic			77,313		77,039
Diluted			82,945		82,412
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 | Software license
Revenue:
Total revenue			$ 61,037		$ 153,427
Cost of revenue:
Total cost of revenue			1,250		2,550
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 | Maintenance
Revenue:
Total revenue			59,590		118,555
Cost of revenue:
Total cost of revenue			7,011		14,229
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 | Services
Revenue:
Total revenue			77,353		149,245
Cost of revenue:
Total cost of revenue			59,614		119,186
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09
Assets
Accounts receivable, unbilled receivables, and contract assets						134,216
Long-term unbilled receivables						160,708
Deferred income taxes						(42,887)
Deferred contract costs						37,924
Total assets						289,961
Liabilities and stockholders' equity
Deferred revenue						(28,776)
Long-term deferred revenue						(2,885)
Deferred income tax liabilities						38,463
Total liabilities						6,802
Foreign currency translation adjustments						(2,966)
Retained earnings						286,125
Total stockholders' equity						283,159
Total liabilities and stockholders' equity						$ 289,961
Revenue:
Total revenue			(11,384)		21,678
Cost of revenue:
Gross profit			(11,384)		21,678
Operating expenses:
Selling and marketing			(687)		(2,294)
Total operating expenses			(687)		(2,294)
Income/(loss) from operations			(10,697)		23,972
Foreign currency transaction loss			(1,325)		(1,256)
Interest income, net			41		81
Income/(loss) before benefit from income taxes			(11,981)		22,797
Benefit from income taxes			(4,277)		4,559
Net income			(7,704)		18,238
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 | Software license
Revenue:
Total revenue			(9,887)		24,731
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 | Maintenance
Revenue:
Total revenue			(166)		(418)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 | Services
Revenue:
Total revenue			$ (1,331)		$ (2,635)

[1] On January 1, 2018 the Company adopted the ASC 606 revenue recognition standard and has adjusted prior periods to conform. See Note 2. "New Accounting Pronouncements" for additional information.

[2] Includes cash, cash equivalents, marketable securities, income taxes receivable, other current assets, property and equipment, intangible assets, goodwill, and other long-term assets (as reflected in the consolidated balance sheets in the Annual Report on Form 10-K for the year ended December 31, 2017).

[3] Included in other long-term liabilities in the unaudited condensed consolidated balance sheets.

[4] Includes accounts payable, accrued expenses, accrued compensation and related expenses, income taxes payable, and other long-term liabilities (as reflected in the consolidated balance sheets in the Annual Report on Form 10-K for the year ended December 31, 2017).

[5] Includes common stock, additional paid-in capital, and net unrealized loss on available-for-sale marketable securities (as reflected in the consolidated balance sheets in the Annual Report on Form 10-K for the year ended December 31, 2017).