Aggregate dividends declared 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

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

EQUITY STRUCTURE AND ACCOUNTS - Dividends Declared (Details) - $ / shares													3 Months Ended								12 Months Ended
	Nov. 07, 2017	Sep. 01, 2017	Jun. 01, 2017	Mar. 01, 2017	Dec. 02, 2016	Sep. 01, 2016	Jun. 01, 2016	Apr. 01, 2016	Dec. 01, 2015	Sep. 01, 2015	Jun. 08, 2015	Mar. 12, 2015	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
Class of Stock [Line Items]
Dividends per share of common stock (in dollars per share)													$ 0.315	$ 0.3	$ 0.3	$ 0.3	$ 0.46	$ 0.275	$ 0.275	$ 0.275
Class A common stock
Class of Stock [Line Items]
Dividends per share of common stock (in dollars per share)	$ 0.315	$ 0.3	$ 0.3	$ 0.3	$ 0.46	$ 0.275	$ 0.275	$ 0.275	$ 1.45	$ 0.275	$ 0.25	$ 0.25									$ 1.215	$ 1.285	$ 2.225