Dividends and Earnings Per Share - Dilutive Effect (Details) - Equity Plan - Restricted Stock Units - shares	6 Months Ended	38 Months Ended	50 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017
Earnings per share
Units granted	259,065	259,065	259,065
Accrued Dividend Equivalent Units	2,378		2,378

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration