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 - Additional Information (Detail) - $ / shares					3 Months Ended		9 Months Ended
	Nov. 01, 2018	Aug. 08, 2018	May 02, 2018	Feb. 14, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)		$ 2.28	$ 2.28	$ 2.28	$ 2.28	$ 2.00	$ 6.84	$ 6.00
Subsequent event [Member]
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)	$ 2.28