Summary of Impact of Adoption of ASU 606 (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Assets
Accounts receivable, unbilled receivables, and contract assets						$ 382,547
Long-term unbilled receivables	[1]	$ 168,929		$ 168,929		160,708
Deferred income taxes						14,240
Deferred contract costs						37,924
Other assets	[2]					416,148
Total assets	[1]	962,643		962,643		1,011,567
Liabilities and stockholders' equity
Deferred revenue	[1]	158,178		158,178		166,297
Long-term deferred revenue	[3]	5,840		5,840		3,706
Deferred income tax liabilities	[1]	36,166		36,166		38,463
Other liabilities	[4]					148,864
Total liabilities	[1]	341,788		341,788		357,330
Foreign currency translation adjustments						(6,460)
Retained earnings	[1]	496,815		496,815		508,051
Other equity	[5]					152,646
Total stockholders' equity	[1]	620,855		620,855		654,237
Total liabilities and stockholders' equity	[1]	962,643		962,643		1,011,567
Revenue:
Total revenue	[1]	203,263	$ 190,957	635,224	$ 633,862
Cost of revenue:
Total cost of revenue	[1]	74,423	69,731	223,854	205,696
Gross profit	[1]	128,840	121,226	411,370	428,166
Operating expenses:
Selling and marketing	[1]	87,490	69,363	269,845	214,244
Research and development	[1]	46,504	41,031	135,261	121,089
General and administrative	[1]	12,104	13,133	38,749	38,174
Total operating expenses	[1]	146,098	123,527	443,855	373,507
(Loss) income from operations	[1]	(17,258)	(2,301)	(32,485)	54,659
Foreign currency transaction loss	[1]	399	(5,052)	558	(6,549)
Interest income, net	[1]	683	140	2,076	547
Other income, net	[1]			363	287
(Loss) income before benefit from income taxes	[1]	(16,176)	(7,213)	(29,488)	48,944
Benefit from income taxes	[1]	(8,589)	(8,501)	(23,692)	(9,009)
Net (loss) income	[1]	$ (7,587)	$ 1,288	$ (5,796)	$ 57,953
(Loss) earnings per share:
Basic	[1]	$ (0.10)	$ 0.01	$ (0.07)	$ 0.75
Diluted	[1]	$ (0.10)	$ 0.01	$ (0.07)	$ 0.70
Weighted-average number of common shares outstanding:
Basic	[1]	78,700	77,691	78,525	77,258
Diluted	[1]	78,700	83,323	78,525	82,717
Software license
Revenue:
Total revenue	[1]	$ 52,342	$ 53,234	$ 184,899	$ 231,392
Cost of revenue:
Total cost of revenue	[1]	1,255	1,276	3,772	3,826
Maintenance
Revenue:
Total revenue	[1]	66,017	61,812	196,448	179,949
Cost of revenue:
Total cost of revenue	[1]	6,079	6,716	18,035	20,945
Services
Revenue:
Total revenue	[1]	84,904	75,911	253,877	222,521
Cost of revenue:
Total cost of revenue	[1]	$ 67,089	61,739	$ 202,047	180,925
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			179,815		601,042
Cost of revenue:
Total cost of revenue			69,731		205,696
Gross profit			110,084		395,346
Operating expenses:
Selling and marketing			70,209		217,384
Research and development			41,031		121,089
General and administrative			13,133		38,174
Total operating expenses			124,373		376,647
(Loss) income from operations			(14,289)		18,699
Foreign currency transaction loss			(552)		(793)
Interest income, net			144		470
Other income, net					287
(Loss) income before benefit from income taxes			(14,697)		18,663
Benefit from income taxes			(12,885)		(17,952)
Net (loss) income			$ (1,812)		$ 36,615
(Loss) earnings per share:
Basic			$ (0.03)		$ 0.47
Diluted			$ (0.03)		$ 0.44
Weighted-average number of common shares outstanding:
Basic			77,691		77,258
Diluted			77,691		82,717
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 | Software license
Revenue:
Total revenue			$ 41,793		$ 195,220
Cost of revenue:
Total cost of revenue			1,276		3,826
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 | Maintenance
Revenue:
Total revenue			62,204		180,759
Cost of revenue:
Total cost of revenue			6,716		20,945
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 | Services
Revenue:
Total revenue			75,818		225,063
Cost of revenue:
Total cost of revenue			61,739		180,925
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			11,142		32,820
Cost of revenue:
Gross profit			11,142		32,820
Operating expenses:
Selling and marketing			(846)		(3,140)
Total operating expenses			(846)		(3,140)
(Loss) income from operations			11,988		35,960
Foreign currency transaction loss			(4,500)		(5,756)
Interest income, net			(4)		77
(Loss) income before benefit from income taxes			7,484		30,281
Benefit from income taxes			4,384		8,943
Net (loss) income			3,100		21,338
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 | Software license
Revenue:
Total revenue			11,441		36,172
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 | Maintenance
Revenue:
Total revenue			(392)		(810)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 | Services
Revenue:
Total revenue			$ 93		$ (2,542)

[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.

[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).