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Retirement and Share-based Compensation Plans (Defined Contribution Plan) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement [Abstract]
Defined contribution plan, maximum annual employee contribution	$ 19,500	$ 19,000	$ 18,500
Defined contribution plan, employer plan contributions	$ 2,400,000	$ 1,800,000	$ 1,700,000

X

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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X

- Definition

Maximum amount the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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X

- References

No definition available.

+ Details

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