Aggregate dividends paid during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Subsequent Events (Details) - $ / shares			3 Months Ended								12 Months Ended
Subsequent Events (Details) - $ / shares	Feb. 15, 2018	Jan. 25, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent events
Dividends declared per common share (in dollars per share)			$ 0.2	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.8	$ 0.8	$ 0.8
Subsequent Event
Subsequent events
Dividends declared per common share (in dollars per share)		$ 0.20
Dividends paid per common share (in dollars per share)	$ 0.20