Dividends - Schedule of Dividends (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Jun. 30, 2016
Equity [Abstract]
Cash dividends paid per common share (in dollars per share)	$ 0.18750	$ 0.18625
Total cash dividends paid	$ 13,750	$ 13,624	$ 27,374	$ 26,451

Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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