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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

Subsequent events (Details) - $ / shares		3 Months Ended
Subsequent events (Details) - $ / shares	Feb. 05, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
Subsequent Event [Line Items]
Dividends declared (in dollars per share)		$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.71	$ 0.21	$ 0.21	$ 0.21
Subsequent Event
Subsequent Event [Line Items]
Dividends declared (in dollars per share)	$ 0.21