Dividends - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2019
Dividends [Abstract]
Dividends declared and paid	$ 17.3	$ 17.6	$ 35.6
Dividends declared and paid, per share	$ 0.20	$ 0.20

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

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_DividendsCommonStockCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration