Borrowings (Interest Rates and Company Borrowings) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest and debt expense:
Weighted average interest rate during the quarter	3.06%	2.43%	3.08%	2.34%
Interest rate at quarter end	2.81%	2.43%	2.81%	2.43%
Maximum amount outstanding during the quarter	$ 705,000	$ 538,000	$ 705,000	$ 538,000
Average amount outstanding during the quarter	585,924	516,946	542,186	508,350
Facility fees	$ 128	$ 49	$ 272	$ 125

The average effective interest rate during the reporting period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 210
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-Section S99
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-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Average amount borrowed under the credit facility during the period.

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Amount of the fees associated with providing collateral for the credit facility.

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The effective interest rate during the reporting period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
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Maximum amount borrowed under the credit facility at any time during the period.

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