Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net income	$ 80,486	$ 62,089
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	9,483	9,221
Stock-based compensation expense	7,468	6,937
Deferred taxes	1,399	307
Other	740	9,219
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(4,669)	(22,677)
(Increase) in prepaid expenses and other assets	(9,407)	(3,574)
(Decrease) in accrued employee compensation	(11,703)	(9,084)
(Decrease) in income and other tax liabilities	(3,068)	(1,856)
Increase in deferred revenue	561	294
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(441)	2,708
Net cash provided by (used in) operating activities	69,118	(20,096)
Cash flows from investing activities
Proceeds from maturities and sales, available-for-sale investments	101,354	20,000
Purchases, available-for-sale investments	(143,214)	(8,065)
Purchases of furniture, equipment and leasehold improvements	(5,777)	(3,904)
Capitalization of software development costs	(6,667)	(6,142)
Other	(33)	99
Net cash (used in) provided by investing activities	(54,337)	1,988
Cash flows from financing activities
Cash dividend on common stock	(24,535)	(19,313)
Exercise of stock options	1,338	2,138
Withholding tax payments on restricted stock vesting and stock option exercises	(8,111)	(5,585)
Repurchases of common stock	(24,147)	(5,400)
Net cash (used in) financing activities	(55,455)	(28,160)
Effect of exchange rate changes on cash and cash equivalents	574	(185)
Cash and cash equivalents
Net (decrease) for the period	(40,100)	(46,453)
Beginning of period	168,243	199,728
End of period	128,143	153,275
Corporate Debt [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	(111)	(72,396)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	$ (1,620)	$ (1,284)