Consolidated Statements of Stockholders' Equity and Redeemable Noncontrolling Interests - 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, 2018	$ 997	$ 311,264	$ 1,198,445	$ (627,587)	$ 331	$ 883,450
Balance (in shares) at Dec. 31, 2018	99,701
Increase (Decrease) in Stockholders' Equity
Net income (loss)			32,053			32,053
Recognition of equity compensation		9,608	93			9,701
Net issuance/forfeiture of nonvested shares		(30,000)		30,000
Dividends accrued			(19,025)			(19,025)
Repurchase of common stock				(39,139)		(39,139)
Other comprehensive income (loss)					1,564	1,564
Balance at the end of the period at Mar. 31, 2019	$ 997	290,872	1,211,566	(636,726)	1,895	868,604
Balance (in shares) at Mar. 31, 2019	99,701
Balance at the beginning of the period at Dec. 31, 2018						11,463
Increase (Decrease) in Redeemable Noncontrolling Interest
Net income (loss)						705
Net subscription of redeemable noncontrolling interests in sponsored funds						768
Balance at the end of the period at Mar. 31, 2019						12,936
Balance at the beginning 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 Stockholders' Equity
Net income (loss)			21,986			21,986
Recognition of equity compensation		7,693	71			7,764
Net issuance/forfeiture of nonvested shares		(37,985)		37,985
Dividends accrued			(16,571)			(16,571)
Repurchase of common stock				(53,939)		(53,939)
Other comprehensive income (loss)					(2,479)	(2,479)
Balance at the end of the period at Mar. 31, 2020	$ 997	$ 282,401	$ 1,247,084	$ (765,579)	$ 755	765,658
Balance (in shares) at Mar. 31, 2020	99,701
Balance at the beginning of the period at Dec. 31, 2019						19,205
Increase (Decrease) in Redeemable Noncontrolling Interest
Net income (loss)						(1,522)
Net subscription of redeemable noncontrolling interests in sponsored funds						1,387
Balance at the end of the period at Mar. 31, 2020						$ 19,070