Financial Instruments and Fair Value Measurements - Schedule of Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Fair value, asset derivatives	$ 2,921	$ 818
Fair value, liability derivatives	(3,590)	(5,876)
Core Portfolio [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	331,058
Fair value, derivatives, net	(609)	(4,440)
Core Portfolio [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	140,651
Fair value, liability derivatives	$ (3,218)	(5,255)
Core Portfolio [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	1.38%
Core Portfolio [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	3.77%
Core Portfolio [Member] \| Interest Rate Swap [Member] \| Other Assets [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	$ 190,407
Fair value, asset derivatives	$ 2,609	815
Core Portfolio [Member] \| Interest Rate Swap [Member] \| Other Assets [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	1.24%
Core Portfolio [Member] \| Interest Rate Swap [Member] \| Other Assets [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	3.77%
Fund II [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	$ 49,279
Fair value, derivatives, net	(228)	(382)
Fund II [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	19,779
Fund II [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, liability derivatives	$ (228)	(385)
Fund II [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	2.88%
Fund II [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	2.88%
Fund II [Member] \| Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	$ 29,500
Fund II [Member] \| Interest Rate Cap [Member] \| Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, asset derivatives	$ 0	3
Fund II [Member] \| Interest Rate Cap [Member] \| Other Assets [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	4.00%
Fund II [Member] \| Interest Rate Cap [Member] \| Other Assets [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	4.00%
Fund III [Member] \| Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	$ 58,000
Fund III [Member] \| Interest Rate Cap [Member] \| Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, asset derivatives	$ 127	0
Fund III [Member] \| Interest Rate Cap [Member] \| Other Assets [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	3.00%
Fund III [Member] \| Interest Rate Cap [Member] \| Other Assets [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	3.00%
Fund IV [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	$ 123,409
Fair value, derivatives, net	41	(236)
Fund IV [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	14,509
Fund IV [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value, liability derivatives	$ (144)	(236)
Fund IV [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	1.78%
Fund IV [Member] \| Interest Rate Swap [Member] \| Other Liabilities [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	1.78%
Fund IV [Member] \| Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Aggregate Notional Amount	$ 108,900
Fund IV [Member] \| Interest Rate Cap [Member] \| Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value, asset derivatives	$ 185	$ 0
Fund IV [Member] \| Interest Rate Cap [Member] \| Other Assets [Member] \| Minimum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	3.00%
Fund IV [Member] \| Interest Rate Cap [Member] \| Other Assets [Member] \| Maximum [Member]
Derivatives, Fair Value [Line Items]
Strike Rate	3.00%

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Variable interest rate in effect as of the balance sheet date related to the interest rate derivative.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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