Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 58,940	$ 39,101	$ 32,994
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization	14,605	13,786	12,711
Share-based compensation expense	14,819	11,653	7,411
Provision for losses - accounts receivable	1,897	729	961
Excess tax benefit from exercises of share-based arrangements	(19,402)	(28,207)	(8,764)
Deferred income tax benefit	(3,804)	(1,497)	(215)
Changes in operating assets and liabilities, exclusive of effects of acquired companies:
Accounts receivable	(8,912)	(7,488)	(6,825)
Income tax receivable	29,117	18,898	7,791
Prepaid expenses and other current assets	(3,696)	(4,154)	110
Accounts payable	1,586	(574)	(369)
Accrued liabilities	6,326	7,655	(530)
Deferred revenue	31,961	16,188	13,393
Net cash provided by operating activities	123,437	66,090	58,668
Cash flows from investing activities:
Proceeds from sale of investments	808	1,090	75
Cost of acquisitions, net of cash acquired	(3,242)	(181)	(25,680)
Additions to property and equipment	(9,343)	(26,858)	(9,102)
Decrease (increase) in other	222	291	(29)
Net cash used by investing activities	(11,555)	(25,658)	(34,736)
Cash flows from financing activities:
Purchase of treasury shares	(22,817)
Contributions from employee stock purchase plan	4,144	3,542	2,641
Proceeds from exercise of stock options	14,680	18,289	12,443
Decrease in net borrowings on revolving line of credit		(18,000)	(42,700)
Excess tax benefit from exercises of share-based arrangements	19,402	28,207	8,764
Net cash provided (used) by financing activities	15,409	32,038	(18,852)
Net increase in cash and cash equivalents	127,291	72,470	5,080
Cash and cash equivalents at beginning of period	78,876	6,406	1,326
Cash and cash equivalents at end of period	$ 206,167	$ 78,876	$ 6,406