Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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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 Accounting Standards Codification
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-SubTopic 10
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Name:	us-gaap_StockRepurchasedDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Common Stock (Details) - USD ($)	1 Months Ended	12 Months Ended
Common Stock (Details) - USD ($)	Mar. 31, 2009	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2008
Class of Stock Disclosures [Abstract]
Total purchased shares (in shares)	859,499	0	0
Additional estimated shares (in shares)		124,740
Closing price (in dollars per share)		$ 120.25
Maximum [Member]
Class of Stock Disclosures [Abstract]
Common stock authorized by the Board of Directors (in shares)	1,200,000			2,250,000
Percentage of repurchase of common stock	10.00%
Bank credit agreement to permit share repurchases of common stock	$ 15,000,000