Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Summary of Significant Accounting Policies - Debt (Details) - Senior Notes [Member] - USD ($)	Feb. 28, 2018	Feb. 28, 2017	Jan. 21, 2011
Unsecured Senior Notes Due March 31, 2018 [Member]
Debt Instrument [Line Items]
Fair value of notes	$ 133,659,750	$ 144,350,531
Unsecured Senior Notes Due January 2021 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 125,000,000