Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net income	$ 42,463	$ 28,963
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,693	4,681
Stock-based compensation expense	3,943	3,494
Deferred taxes	1,827	2,331
Other	393	4,969
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(6,113)	(12,346)
(Increase) in prepaid expenses and other assets	(2,146)	(3,000)
(Decrease) in accrued employee compensation	(20,911)	(18,386)
Increase in income and other tax liabilities	7,366	6,026
Increase in deferred revenue	675	290
Increase in accounts payable, accrued expenses and other liabilities	1,074	4,723
Net cash provided by (used in) operating activities	30,549	(52,743)
Cash flows from investing activities
Proceeds from maturities, available-for-sale investments	46,485	12,000
Purchases, available-for-sale investments	(68,166)
Purchases of furniture, equipment and leasehold improvements	(4,149)	(2,652)
Capitalization of software development costs	(3,172)	(3,035)
Other	(5)	26
Net cash (used in) provided by investing activities	(29,007)	6,339
Cash flows from financing activities
Cash dividend on common stock	(12,356)	(9,727)
Exercise of stock options	500	831
Withholding tax payments on restricted stock vesting and stock option exercises	(7,642)	(5,230)
Repurchases of common stock	(12,207)	(1,199)
Net cash (used in) financing activities	(31,705)	(15,325)
Effect of exchange rate changes on cash and cash equivalents	(425)	(4)
Cash and cash equivalents
Net (decrease) for the period	(30,588)	(61,733)
Beginning of period	168,243	199,728
End of period	137,655	137,995
Corporate Debt [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	(1,196)	(73,235)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	$ (1,519)	$ (1,253)