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		28,109
Net realized gain (loss) on investments, financial derivatives, and foreign currency transactions		(4,973)
Change in net unrealized gain (loss) on investments, other secured borrowings, financial derivatives, and foreign currency translation		4,630
Net Income (Loss) Attributable to Parent		26,537		26,537
Net Income (Loss) Attributable to Noncontrolling Interest		1,229			1,229
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		27,766
Shares Issued As Payment of Incentive Fee		0		0
CHANGE IN EQUITY RESULTING FROM TRANSACTIONS
Contributions from non-controlling interests		14,201			14,201
Dividends	[1]	(44,336)	[2]	(44,050)	(286)
Distributions to non-controlling interest		(8,178)			(8,178)
Adjustment to non-controlling interest		0		(6)	6
Shares repurchased		(4,791)		(4,791)
Share-based LTIP awards		285		284	1
Net increase (decrease) in equity from transactions		(42,819)		(48,563)	5,744
Net increase (decrease) in equity		(15,053)		(22,026)	6,973
Stockholders' Equity Attributable to Parent at Sep. 30, 2017				615,635
Stockholders' Equity Attributable to Noncontrolling Interest at Sep. 30, 2017					14,089
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Sep. 30, 2017		629,724
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		32,911
Net realized gain (loss) on investments, financial derivatives, and foreign currency transactions		21,810
Change in net unrealized gain (loss) on investments, other secured borrowings, financial derivatives, and foreign currency translation		(3,740)
Net Income (Loss) Attributable to Parent		48,892		48,892
Net Income (Loss) Attributable to Noncontrolling Interest		2,089			2,089
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		50,981
Shares Issued As Payment of Incentive Fee		29		29
CHANGE IN EQUITY RESULTING FROM TRANSACTIONS
Contributions from non-controlling interests		11,900			11,900
Dividends	[1]	(38,152)	[2]	(37,891)	(261)
Distributions to non-controlling interest		(11,744)			(11,744)
Adjustment to non-controlling interest		0		(33)	33
Shares repurchased		(17,593)		(17,593)
Share-based LTIP awards		296		294	2
Net increase (decrease) in equity from transactions		(55,264)		(55,194)	(70)
Net increase (decrease) in equity		(4,283)		(6,302)	2,019
Stockholders' Equity Attributable to Parent at Sep. 30, 2018		593,797		$ 593,797
Stockholders' Equity Attributable to Noncontrolling Interest at Sep. 30, 2018		22,881			$ 22,881
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Sep. 30, 2018		$ 616,678

[1] For the nine-month periods ended September 30, 2018 and 2017, dividends totaling $1.23 and $1.35, respectively, per common share and convertible unit outstanding, were declared.

[2] The Company pays quarterly dividends in arrears, so a portion of the dividends paid in each calendar year relate to the prior year's earnings.