Stock Plans and Stock Based Compensation - Net Cash Proceeds, Tax Benefits and Intrinsic Value Related to Stock Options, SARs, and Restricted Stock (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement [Abstract]
Proceeds from stock option exercises	$ (253)	$ (992)	$ (540)
Tax benefits related to stock option exercises	156	944	680
Intrinsic value of stock option exercises	$ 570	$ 2,460	$ 1,447

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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Balance Type:	debit
Period Type:	duration