Consolidated Statement of Stockholders’ Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income(Loss)	Total
Balance at the beginning of the period at Dec. 31, 2016					$ (6,757)
Increase (Decrease) in Stockholders' Equity
Net income						$ 33,871
Balance at the end of the period at Mar. 31, 2017					(3,187)
Balance at the beginning of the period at Dec. 31, 2017	$ 997	$ 301,410	$ 1,092,394	$ (522,441)	524	872,884
Balance (in shares) at Dec. 31, 2017	99,701
Increase (Decrease) in Stockholders' Equity
Adoption of ASU guidance on January 1, 2018 | ASU 2016-01			812		(812)
Adoption of ASU guidance on January 1, 2018 | ASU 2018-02			36		(36)
Adoption of ASU guidance on January 1, 2018					(848)
Net income			46,337			46,337
Recognition of equity compensation		12,065	209			12,274
Net issuance/forfeiture of nonvested shares		(29,707)		29,707
Dividends accrued, $0.25 per share			(20,866)			(20,866)
Repurchase of common stock				(20,507)		(20,507)
Other comprehensive loss					(1,154)	(1,154)
Balance at the end of the period at Mar. 31, 2018	$ 997	$ 283,768	$ 1,118,922	$ (513,241)	$ (1,478)	888,968
Balance (in shares) at Mar. 31, 2018	99,701
Balance at the beginning of the period at Dec. 31, 2017						14,509
Increase (Decrease) in Redeemable Noncontrolling Interest
Net income						(366)
Net redemption of redeemable noncontrolling interests in sponsored funds						4,427
Balance at the end of the period at Mar. 31, 2018						$ 18,570