Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 26,155,000	$ 80,052,000	$ 61,051,000
Non-cash items included in net income:
Income tax expense	12,900,000	53,018,000	12,403,000
Depreciation and amortization	1,305,000	1,006,000	821,000
Stock-based compensation	14,892,000	10,900,000	8,137,000
Goodwill impairment	1,676,000
Deferred rent	(231,000)	(83,000)	1,572,000
Accretion to interest income and other	(47,000)	4,000	(72,000)
Changes in operating assets and liabilities:
Securities owned, at fair value	(1,556,000)
Accounts receivable	9,778,000	(9,321,000)	(369,000)
Prepaid expenses	(719,000)	(1,069,000)	(258,000)
Other assets	(307,000)	(795,000)	357,000
Acquisition payable	(384,000)	2,185,000
Fund management and administration payable	9,636,000	2,978,000	(445,000)
Compensation and benefits payable	(13,089,000)	13,286,000	(186,000)
Income taxes payable	1,687,000	2,974,000	10,000
Securities sold, but not yet purchased, at fair value	1,249,000
Accounts payable and other liabilities	(8,034,000)	(24,000)	(391,000)
Net cash provided by operating activities	54,911,000	155,111,000	82,630,000
Cash flows from investing activities:
Purchase of fixed assets	(1,070,000)	(2,616,000)	(4,894,000)
Purchase of securities held-to-maturity	(15,502,000)	(14,467,000)	(3,225,000)
Purchase of securities available-for-sale	(63,619,000)
Purchase of investment	(20,000,000)
Proceeds from held-to-maturity securities maturing or called prior to maturity	16,742,000	4,764,000	939,000
Proceeds from sales and maturities of securities available-for-sale	6,002,000
Acquisition less cash acquired	(11,818,000)		1,349,000
Net cash used in investing activities	(89,265,000)	(12,319,000)	(5,831,000)
Cash flows from financing activities:
Dividends paid	(43,660,000)	(78,540,000)	(10,785,000)
Shares repurchased	(39,379,000)	(24,116,000)	(6,531,000)
Proceeds from exercise of stock options	195,000	4,520,000	1,544,000
Net cash used in financing activities	(82,844,000)	(98,136,000)	(15,772,000)
(Decrease)/increase in cash flow due to changes in foreign exchange rate	(150,000)	130,000	(59,000)
Net (decrease)/increase in cash and cash equivalents	(117,348,000)	44,786,000	60,968,000
Cash and cash equivalents-beginning of year	210,070,000	165,284,000	104,316,000
Cash and cash equivalents-end of year	92,722,000	210,070,000	165,284,000
Supplemental disclosure of cash flow information:
Cash paid for taxes	$ 14,990,000	$ 1,262,000	$ 66,000