Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 64,869	$ 58,940	$ 39,101
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization	19,574	14,605	13,786
Share-based compensation expense	20,182	14,819	11,653
Provision for losses - accounts receivable	1,756	1,897	729
Excess tax benefit from exercises of share-based arrangements	(45,314)	(19,402)	(28,207)
Deferred income tax benefit	(7,956)	(3,804)	(1,497)
Changes in operating assets and liabilities, exclusive of effects of acquired companies:
Accounts receivable	(28,172)	(8,912)	(7,488)
Income tax receivable	24,255	29,117	18,898
Prepaid expenses and other current assets	(3,054)	(3,696)	(4,154)
Accounts payable	652	1,586	(574)
Accrued liabilities	490	6,326	7,655
Deferred revenue	41,731	31,961	16,188
Net cash provided by operating activities	89,013	123,437	66,090
Cash flows from investing activities:
Cost of acquisitions, net of cash acquired	(339,961)	(3,242)	(181)
Purchase of cost method investment	(15,000)
Purchase of marketable security investments	(31,907)
Proceeds from marketable security investments	900	808	1,090
Additions to property and equipment	(12,501)	(9,343)	(26,858)
Decrease in other	10	222	291
Net cash used by investing activities	(398,459)	(11,555)	(25,658)
Cash flows from financing activities:
Increase (decrease) in net borrowings on revolving line of credit	66,000		(18,000)
Purchase of treasury shares	(645)	(22,817)
Contributions from employee stock purchase plan	4,671	4,144	3,542
Proceeds from exercise of stock options	23,160	14,680	18,289
Debt issuance costs	(2,134)
Excess tax benefit from exercises of share-based arrangements	45,314	19,402	28,207
Net cash provided by financing activities	136,366	15,409	32,038
Net (decrease) increase in cash and cash equivalents	(173,080)	127,291	72,470
Cash and cash equivalents at beginning of period	206,167	78,876	6,406
Cash and cash equivalents at end of period	$ 33,087	$ 206,167	$ 78,876