CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ 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
Revenue
Total revenue		$ 256,357	$ 203,263	$ 196,779	$ 235,182	$ 254,605	$ 190,957	$ 186,596	$ 256,309	$ 891,581	[1]	$ 888,467	[1]	$ 762,229	[1]
Cost of revenue
Total cost of revenue	[1]									301,765		279,673		239,256
Gross profit		178,446	128,840	122,962	159,568	180,628	121,226	118,721	188,219	589,816	[1]	608,794	[1]	522,973	[1]
Operating expenses
Selling and marketing	[1]									373,495		300,578		277,927
Research and development	[1]									181,710		162,886		145,548
General and administrative	[1]									51,643		52,153		45,951
Acquisition-related	[1]									0		0		2,903
Total operating expenses	[1]									606,848		515,617		472,329
(Loss) income from operations		15,453	(17,258)	(23,163)	7,936	38,518	(2,301)	(8,947)	65,907	(17,032)	[1]	93,177	[1]	50,644	[1]
Foreign currency transaction gain (loss)	[1],[2]									2,421		(6,413)		9,360
Interest income, net	[1]									2,705		862		911
Other income (expense), net	[1]									363		(1,391)		(5,580)
(Loss) income before (benefit) provision from income taxes	[1]									(11,543)		86,235		55,335
(Benefit) provision from income taxes	[1]									(22,160)		(12,313)		10,320
Net income		$ 16,413	$ (7,587)	$ (10,409)	$ 12,200	$ 40,595	$ 1,288	$ 3,702	$ 52,963	$ 10,617	[1],[2],[3],[4]	$ 98,548	[1],[2],[3],[4]	$ 45,015	[1],[2],[3],[4]
Earnings per share:
Basic (dollars per share)		$ 0.21	$ (0.10)	$ (0.13)	$ 0.16	$ 0.52	$ 0.01	$ 0.05	$ 0.69	$ 0.14	[1]	$ 1.27	[1]	$ 0.59	[1]
Diluted (dollars per share)		$ 0.20	$ (0.10)	$ (0.13)	$ 0.15	$ 0.49	$ 0.01	$ 0.04	$ 0.65	$ 0.13	[1]	$ 1.19	[1]	$ 0.56	[1]
Weighted-average number of common shares outstanding
Basic (shares)	[1]									78,564		77,431		76,343
Diluted (shares)	[1]									83,064		82,832		79,732
Software license
Revenue
Total revenue	[1]									$ 288,119		$ 339,294		$ 297,284
Cost of revenue
Total cost of revenue	[1]									5,169		5,085		4,943
Maintenance
Revenue
Total revenue	[1]									263,875		242,320		218,635
Cost of revenue
Total cost of revenue	[1]									24,565		27,905		25,505
Services
Revenue
Total revenue	[1]									339,587		306,853		246,310
Cost of revenue
Total cost of revenue	[1]									$ 272,031		$ 246,683		$ 208,808

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

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

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

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