Number of shares that have been repurchased during the period and are being held in treasury.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Name:	us-gaap_TreasuryStockSharesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Earnings Per Share - Additional Information (Detail) - 2011 Share Repurchase Program [Member] - shares	3 Months Ended		6 Months Ended		106 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Mar. 16, 2016	Aug. 18, 2011
Equity, Class of Treasury Stock [Line Items]
Maximum amount of shares authorized for repurchase						10,000,000.0	5,000,000.0
Total Number of Shares Repurchased	500,000	771,000	1,360,000	771,000	7,800,000
Increase in shares authorized for repurchase						5,000,000.0