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

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Date the declared dividend will be paid, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared, for example, but not limited to, common and preferred stock.

+ References

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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6957935&loc=d3e64057-112817

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Date the dividend to be paid was declared, in CCYY-MM-DD format.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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CAPITAL STOCK - Cash dividends declared (Details) - USD ($)	3 Months Ended		12 Months Ended						71 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2018
Dividends Payable [Line Items]
Per Share Amount	$ 0.24	$ 0.31
Dividend Declared [Member]
Dividends Payable [Line Items]
Per Share Amount	$ 0.32		$ 1.07	$ 1.68	$ 1.68	$ 1.92	$ 2.16	$ 1.395	$ 10.225
Total	$ 15,824,000		$ 55,814,000	$ 70,717,000	$ 41,388,000	$ 38,748,000	$ 22,643,000	$ 4,662,000	$ 249,796,000
Dividend Declared [Member] \| Subsequent Event [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared	Apr. 17, 2019
Dividends Payable, Date to be Paid	May 31, 2019
Per Share Amount	$ 0.08