Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income		$ 1,670	$ 481
Adjustments to reconcile net income (loss) to net cash (used in) provided by operating activities:
Amortization of intangible assets and depreciation		5,190	5,144
Stock-based compensation	[1]	25,806	18,329
Amortization of discounts or premiums on marketable securities		2,502	2,714
Deferred income taxes		(5,846)	(3,146)
Amortization of debt issuance costs		639	639
Amortization of debt discount		5,862	5,523
Excess tax benefit associated with equity awards		(3,712)	(2,648)
Provision for doubtful accounts		550	266
Changes in operating assets and liabilities:
Accounts receivable		(33,894)	(18,328)
Prepaid commission expense		(123)	657
Prepaid expenses and other current assets		(3,303)	1,018
Other assets		1,497	87
Accounts payable		(702)	2,476
Accrued payroll and other compensation		196	(7,134)
Accrued expenses and other		4,439	5,437
Deferred revenue		27,085	3,588
Other long-term liabilities		889	2,711
Net cash provided by operating activities		28,745	17,814
Cash flows from investing activities:
Purchases of furniture, fixtures and equipment		(5,925)	(11,602)
Purchases of available-for-sale securities		(140,856)	(113,019)
Proceeds from sale of available-for-sale securities		(126,632)	(141,214)
Net (increase) decrease in restricted cash		(464)	226
Net cash (used in) provided by investing activities		(20,613)	16,819
Cash flows from financing activities:
Proceeds from exercise of stock options		5,199	1,885
Proceeds from employee stock purchase plan		2,960	2,513
Excess tax benefit associated with equity awards		3,712	2,648
Payment of acquisition-related earn-out		0	(704)
Repayment of obligations under capital leases		(17)	(39)
Repayments of notes payable		0	(85)
Acquisition of treasury stock		(16,154)	(28,058)
Net cash used in financing activities		(4,300)	(21,840)
Effect of exchange rate changes on cash and cash equivalents		17	71
Net increase in cash and cash equivalents		3,849	12,864
Cash and cash equivalents - Beginning of period		39,517	22,328
Cash and cash equivalents - End of period		43,366	35,192
Cash paid during the period for:
Interest		1,438	1,350
Income taxes		281	296
Noncash activities:
Furniture, fixtures, and equipment acquired but not yet paid for at period-end		3,682	1,549
Issuance of notes payable in connection with acquisition-related earn-out payments		$ 0	$ 97

[1] Stock-based compensation expense included in cost of revenues and operating costs and expenses