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
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-Section S99
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Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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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).

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Subsequent Events: (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 26, 2018	Feb. 21, 2018	Feb. 28, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent events
Expected value of dividend to be paid					$ 81,657	$ 68,210	$ 66,314
Stock options
Subsequent events
Granted (in shares)				470,404
Fair value of shares				$ 19,000
Performance conditions \| CEO
Subsequent events
Granted (in shares)			105,000
Subsequent Event
Subsequent events
Quarterly dividend payment approved (per share)		$ 0.50
Subsequent Event \| Stock options
Subsequent events
Granted (in shares)			300,000
Fair value of shares			$ 14,100
Subsequent Event \| Performance conditions \| Executives
Subsequent events
Granted (in shares)			24,050
Subsequent Event \| Expected
Subsequent events
Expected value of dividend to be paid	$ 22,400