Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 28,589	$ 23,618
Adjustments to reconcile net income to net cash provided by operations:
Depreciation and amortization	10,093	9,616
Share-based compensation expense	8,539	5,506
Excess tax benefit from exercises of share-based arrangements	(13,200)	(3,283)
Changes in operating assets and liabilities, exclusive of effects of acquired companies:
Accounts receivable	8,798	14,431
Income tax payable	8,853	2,533
Prepaid expenses and other current assets	(2,750)	(302)
Accounts payable	841	(1,236)
Accrued liabilities	(2,022)	(2,263)
Deferred revenue	10,960	(6,366)
Net cash provided by operating activities	58,701	42,254
Cash flows from investing activities:
Proceeds from sale of investments	50	75
Cost of acquisitions, net of cash acquired	(181)	(15,229)
Additions to property and equipment	(20,262)	(6,351)
Decrease in other	271	41
Net cash used by investing activities	(20,122)	(21,464)
Cash flows from financing activities:
Decrease in net borrowings on revolving line of credit	(18,000)	(32,700)
Contributions from employee stock purchase plan	2,535	1,832
Proceeds from exercise of stock options	9,401	5,572
Excess tax benefits from exercises of share-based arrangements	13,200	3,283
Net cash provided (used) by financing activities	7,136	(22,013)
Net increase (decrease) in cash and cash equivalents	45,715	(1,223)
Cash and cash equivalents at beginning of period	6,406	1,326
Cash and cash equivalents at end of period	$ 52,121	$ 103