Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities
Net income	$ 93,007	$ 71,546
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	13,546	13,857
Stock-based compensation expense	10,636	9,276
Deferred taxes	(1,387)	(1,250)
Other	878	1,638
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(16,439)	(15,595)
(Increase) in prepaid expenses and other assets	(2,151)	(347)
(Decrease) in accrued employee compensation	(750)	(2,472)
(Decrease) in income and other tax liabilities	(843)	(1,309)
Increase (decrease) in deferred revenue	694	(250)
Increase in accounts payable, accrued expenses and other liabilities	2,646	1,244
Net cash provided by operating activities	23,974	76,338
Available-for-sale investments:
Proceeds from maturities and sales	32,025	25,048
Purchases	(42,495)	(57,175)
Purchases of furniture, equipment and leasehold improvements	(4,754)	(3,730)
Capitalization of software development costs	(9,058)	(7,517)
Other	383	(141)
Net cash (used in) investing activities	(23,899)	(43,515)
Cash flows from financing activities
Cash dividend on common stock	(28,914)	(22,201)
Exercise of stock options	2,172	1,530
Withholding tax payments on restricted stock vesting and stock option exercises	(5,929)	(4,450)
Excess tax benefits from stock-based compensation	9,166	4,202
Repurchases of common stock	(13,874)	(20,025)
Net cash (used in) financing activities	(37,379)	(40,944)
Effect of exchange rate changes on cash and cash equivalents	(980)	(427)
Cash and cash equivalents
Net (decrease) for the period	(38,284)	(8,548)
Beginning of period	199,728	168,924
End of period	161,444	$ 160,376
Corporate Debt [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	(74,535)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	$ (1,328)