Consolidated Statements of Cash Flows (Parenthetical)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 30, 2013
Notes \| Notes Due February 1, 2033
Interest rate of notes payable	3.00%	3.00%	3.00%	3.00%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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