Share-Based Compensation - Deferred Compensation Plan (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
SERP expense	$ 5,917	$ 5,468
SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
SERP expense	444	497
Unrealized gain recorded in SERP liability account	$ 3,973	$ 4,964

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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