Stock-Based Compensation - Restricted Stock Grants (Details) - Restricted Stock - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards in the period (in shares)	59,311	55,198	44,505
Weighted average grant date fair value (in usd per share)	$ 28.22	$ 29.84	$ 34.33
Employee \| Four-year vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards in the period (in shares)	26,015	22,403	16,666
Employee \| Performance-based vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards in the period (in shares)	25,001	24,427	20,559
Non-Employee Director \| Two-year vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards in the period (in shares)	8,295	8,368	7,280

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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 (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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