CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 32,306	$ 18,224
Adjustments to reconcile net income to cash provided (used) by operations:
Depreciation and amortization	13,099	12,176
Share-based compensation expense	8,676	6,480
Deferred income tax (benefit) expense	(4,089)	92
Changes in operating assets and liabilities, exclusive of effects of acquired companies:
Accounts receivable	36,514	35,750
Income taxes	7,576	9,187
Prepaid expenses and other current assets	(557)	2,074
Accounts payable	(1,166)	(473)
Accrued liabilities	(15,939)	(11,738)
Deferred revenue	(28,241)	(30,451)
Net cash provided by operating activities	48,179	41,321
Cash flows from investing activities:
Additions to property and equipment	(19,820)	(16,722)
Purchase of marketable security investments	(7,128)	(6,410)
Sale of marketable security investments	6,896	3,025
Cost of acquisitions, net of cash acquired	0	(2,000)
Increase in other	(16)	(49)
Net cash used by investing activities	(20,068)	(22,156)
Cash flows from financing activities:
(Decrease) increase in net borrowings on revolving line of credit	(10,000)	74,000
Purchase of treasury shares	(7,032)	(93,930)
Proceeds from exercise of stock options	14,851	1,781
Contributions from employee stock purchase plan	1,650	1,238
Net cash used by financing activities	(531)	(16,911)
Net increase in cash and cash equivalents	27,580	2,254
Cash and cash equivalents at beginning of period	36,151	33,087
Cash and cash equivalents at end of period	$ 63,731	$ 35,341