Condensed Consolidated Statements of Income (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Interest income	$ 224	$ 20	$ 253	$ 290

Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(b))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration