Consolidated Statements of Stockholders' Equity and Redeemable Noncontrolling Interests - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings Cumulative Effect of ASU Adoption	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income Cumulative Effect of ASU Adoption	Accumulated Other Comprehensive Income	Total
Balance at the beginning of the period (ASU 2016-01) at Dec. 31, 2017			$ 812			$ (812)
Balance at the beginning of the period (ASU 2018-02) at Dec. 31, 2017			$ 36			$ (36)
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
Net income (loss)				183,588				183,588
Recognition of equity compensation		40,598		1,383				41,981
Net issuance/forfeiture of nonvested shares		(30,744)			30,744
Dividends accrued				(79,768)				(79,768)
Repurchase of common stock					(135,890)			(135,890)
Other comprehensive income (loss)							655	655
Balance at the end of the period at Dec. 31, 2018	$ 997	311,264		1,198,445	(627,587)		331	883,450
Balance (in shares) at Dec. 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 (loss)								(776)
Net deconsolidation of redeemable noncontrolling interests in sponsored funds								(2,270)
Balance at the end of the period at Dec. 31, 2018								11,463
Increase (Decrease) in Stockholders' Equity
Net income (loss)				114,992				114,992
Recognition of equity compensation		33,610		423				34,033
Net issuance/forfeiture of nonvested shares		(32,181)			32,181
Dividends accrued				(72,262)				(72,262)
Repurchase of common stock					(154,219)			(154,219)
Other comprehensive income (loss)							2,903	2,903
Balance at the end of the period at Dec. 31, 2019	$ 997	312,693		1,241,598	(749,625)		3,234	808,897
Balance (in shares) at Dec. 31, 2019	99,701
Increase (Decrease) in Redeemable Noncontrolling Interest
Net income (loss)								1,973
Net subscription of redeemable noncontrolling interests in sponsored funds								5,769
Balance at the end of the period at Dec. 31, 2019								19,205
Increase (Decrease) in Stockholders' Equity
Net income (loss)				70,457				70,457
Recognition of equity compensation		27,165		208				27,373
Net issuance/forfeiture of nonvested shares		(36,101)			36,101
Dividends accrued				(63,964)				(63,964)
Repurchase of common stock					(114,669)			(114,669)
Other comprehensive income (loss)							(337)	(337)
Balance at the end of the period at Dec. 31, 2020	$ 997	$ 303,757		$ 1,248,299	$ (828,193)		$ 2,897	727,757
Balance (in shares) at Dec. 31, 2020	99,701
Increase (Decrease) in Redeemable Noncontrolling Interest
Net income (loss)								2,200
Net deconsolidation of redeemable noncontrolling interests in sponsored funds								$ (21,405)