Consolidated Statement Of Changes In Equity - USD ($) $ in Thousands		Total	Parent [Member]	Noncontrolling Interest [Member]
Stockholders' Equity Attributable to Parent at Dec. 31, 2016			$ 637,661
Stockholders' Equity Attributable to Noncontrolling Interest at Dec. 31, 2016				$ 7,116
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2016		$ 644,777
CHANGE IN SHAREHOLDERS’ EQUITY RESULTING FROM OPERATIONS
NET INVESTMENT INCOME		35,168
Net realized gain (loss) on investments, financial derivatives, and foreign currency transactions		(10,804)
Change in net unrealized gain (loss) on investments, other secured borrowings, financial derivatives, and foreign currency translation		11,600
Net Income (Loss) Attributable to Parent		33,981	33,981
Net Income (Loss) Attributable to Noncontrolling Interest		1,983		1,983
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		35,964
Shares Issued As Payment of Incentive Fee		0	0
CHANGE IN EQUITY RESULTING FROM TRANSACTIONS
Contributions from non-controlling interests		20,707		20,707
Dividends	[1]	(57,636)	(57,263)	(373)
Distributions to non-controlling interest		(8,594)		(8,594)
Adjustment to non-controlling interest		0	(21)	21
Share-based long term incentive plan unit redemption and distribution		0	0	0
Shares repurchased		(14,642)	(14,642)
Share-based LTIP awards		385	383	2
Net increase (decrease) in equity from transactions		(59,780)	(71,543)	11,763
Net increase (decrease) in equity		(23,816)	(37,562)	13,746
Stockholders' Equity Attributable to Parent at Dec. 31, 2017		600,099	600,099
Stockholders' Equity Attributable to Noncontrolling Interest at Dec. 31, 2017		20,862		20,862
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2017		620,961
CHANGE IN SHAREHOLDERS’ EQUITY RESULTING FROM OPERATIONS
NET INVESTMENT INCOME		43,125
Net realized gain (loss) on investments, financial derivatives, and foreign currency transactions		31,388
Change in net unrealized gain (loss) on investments, other secured borrowings, financial derivatives, and foreign currency translation		(24,602)
Net Income (Loss) Attributable to Parent		46,676	46,676
Net Income (Loss) Attributable to Noncontrolling Interest		3,235		3,235
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		49,911
Shares Issued As Payment of Incentive Fee		71	71
CHANGE IN EQUITY RESULTING FROM TRANSACTIONS
Contributions from non-controlling interests		21,532		21,532
Dividends	[1]	(50,736)	(50,388)	(348)
Distributions to non-controlling interest		(23,853)		(23,853)
Adjustment to non-controlling interest		0	(369)	369
Share-based long term incentive plan unit redemption and distribution		0	(9,537)	9,537
Shares repurchased		(23,131)	(23,131)
Share-based LTIP awards		415	412	3
Net increase (decrease) in equity from transactions		(75,702)	(82,942)	7,240
Net increase (decrease) in equity		(25,791)	(36,266)	10,475
Stockholders' Equity Attributable to Parent at Dec. 31, 2018		563,833	$ 563,833
Stockholders' Equity Attributable to Noncontrolling Interest at Dec. 31, 2018		31,337		$ 31,337
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2018		$ 595,170

[1] For the years ended December 31, 2018 and 2017, dividends totaling $1.64 and $1.76, respectively, per common share and convertible unit outstanding, were declared.