Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 126,172	$ 96,037	$ 74,806
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	17,838	18,542	17,379
Stock-based compensation expense	14,511	12,519	9,769
Deferred taxes	(2,581)	(2,424)	(374)
Other	1,170	2,049	1,725
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(10,429)	(6,748)	827
(Increase) decrease in prepaid expenses and other assets	(2,125)	(2,662)	3,344
Increase in accrued employee compensation	5,487	3,986	1,309
Increase (decrease) in income and other tax liabilities	3,221	(941)	2,365
Increase (decrease) in deferred revenue	203	(153)	(248)
Increase (decrease) in accounts payable, accrued expenses and other liabilities	2,344	(9)	(950)
Net cash provided by operating activities	80,289	120,196	109,952
Cash flows from investing activities
Proceeds from maturities and sales, available-for-sale investments	46,347	35,248	17,574
Purchase, available-for-sale investments	(81,438)	(57,175)	(16,423)
Purchases of furniture, equipment and leasehold improvements	(6,385)	(4,795)	(4,627)
Capitalization of software development costs	(12,118)	(10,589)	(10,160)
Other	414	(642)	611
Net cash (used in) investing activities	(53,180)	(37,953)	(13,025)
Cash flows from financing activities
Cash dividend on common stock	(38,495)	(29,534)	(23,941)
Exercise of stock options	2,299	1,824	2,511
Withholding tax payments on restricted stock vesting and stock option exercises	(5,173)	(4,496)	(5,020)
Excess tax benefits from stock-based compensation	9,458	4,310	4,243
Repurchases of common stock	(23,925)	(23,158)	(37,974)
Other			(42)
Net cash (used in) financing activities	(55,836)	(51,054)	(60,223)
Effect of exchange rate changes on cash and cash equivalents	(2,758)	(385)	(471)
Cash and cash equivalents
Net (decrease) increase for the period	(31,485)	30,804	36,233
Beginning of period	199,728	168,924	132,691
End of period	168,243	199,728	168,924
Cash paid during the year
Cash paid for income taxes	58,268	$ 50,875	$ 33,627
Corporate Debt [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	(74,195)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) in trading securities	$ (1,327)