Tax Characterization of Dividends per Share on Common Shares (Parenthetical) (Detail) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Dividends Payable [Line Items]
Dividend declared per share	$ 0.44	$ 1.76
Qualified dividend as defined by the IRS
Dividends Payable [Line Items]
Dividend declared per share	0.042774
Qualified dividend as defined by the IRS
Dividends Payable [Line Items]
Dividend declared per share	$ 0.040745

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=120397183&loc=d3e187085-122770

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