Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Net income	$ 103,475	$ 82,000	$ 67,296
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,764	6,377	5,825
Equity-based compensation	14,528	9,671	7,325
(Gain) loss on disposal of equipment	(30)	(13)	31
Tax benefit of stock awards exercised/vested	9,170	8,640	6,980
Excess tax benefits from equity-based compensation	(9,147)	(8,562)	(6,637)
Deferred income taxes	1,532	(1,705)	3,165
Unrealized foreign currency loss (gain)	49	(624)	205
Changes in operating assets and liabilities:
Accounts receivable, net	(12,223)	(16,758)	(9,174)
Other assets	(1,427)	(5,198)	697
Accounts payable, accrued and other liabilities	(1,592)	13,519	3,164
Income taxes	(2,271)	338	4,500
Deferred revenue	10,325	6,477	6,010
Net cash provided by operating activities	120,153	94,162	89,387
Investing activities:
Purchases of property and equipment	(11,492)	(9,415)	(4,740)
Purchases of short-term investments	(15,385)	(14,644)	(14,751)
Maturities of short-term investments	13,334	14,165	11,686
Payment in connection with acquisition		(2,773)
Net cash used in investing activities	(13,543)	(12,667)	(7,805)
Financing activities:
Purchase of common stock	(112,138)	(99,204)	(64,199)
Proceeds from issuance of common stock from options exercised	717	1,571	5,754
Excess tax benefits from equity-based compensation	9,147	8,562	6,637
Net cash used in financing activities	(102,274)	(89,071)	(51,808)
Foreign currency impact on cash	(1,628)	(1,091)	(2,136)
Net change in cash and cash equivalents	2,708	(8,667)	27,638
Cash and cash equivalents at beginning of period	115,708	124,375	96,737
Cash and cash equivalents at end of period	118,416	115,708	124,375
Supplemental disclosures of cash flow information:
Cash paid for taxes	$ 50,902	$ 38,674	$ 21,191