Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities
Net income	$ 28,963	$ 24,593
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,681	4,612
Stock-based compensation expense	3,494	3,042
Deferred taxes	2,331	1,719
Other	329	429
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(12,346)	(12,289)
(Increase) in prepaid expenses and other assets	(3,000)	(541)
(Decrease) in accrued employee compensation	(18,386)	(16,350)
Increase in income and other tax liabilities	6,026	3,710
Increase in deferred revenue	290	260
Increase in accounts payable, accrued expenses and other liabilities	4,723	849
Net cash (used in) provided by operating activities	(57,383)	10,034
Available-for-sale investments:
Proceeds from maturities	12,000	10,515
Purchases		(8,111)
Purchases of furniture, equipment and leasehold improvements	(2,652)	(817)
Capitalization of software development costs	(3,035)	(2,654)
Other	26	19
Net cash provided by (used in) investing activities	6,339	(1,048)
Cash flows from financing activities
Cash dividend on common stock	(9,727)	(7,517)
Exercise of stock options	831	692
Withholding tax payments on restricted stock vesting and stock option exercises	(5,230)	(4,148)
Excess tax benefits from stock-based compensation	4,640	2,671
Repurchases of common stock	(1,199)	(8,939)
Net cash (used in) financing activities	(10,685)	(17,241)
Effect of exchange rate changes on cash and cash equivalents	(4)	379
Cash and cash equivalents
Net (decrease) for the period	(61,733)	(7,876)
Beginning of period	199,728	168,924
End of period	137,995	$ 161,048
Corporate Debt [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	(73,235)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	$ (1,253)