Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12355-112629

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12317-112629

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Name:	us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Debt - Narrative (Details) - USD ($)		3 Months Ended
Debt - Narrative (Details) - USD ($)	Apr. 16, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt [Line Items]
Loss on extinguishment of debt		$ 607,000	$ 0
$600 Million Unsecured Revolving Credit Facility \| Senior
Debt [Line Items]
Letters of credit outstanding, amount		396,800,000
Debt instrument face amount		$ 600,000,000		$ 600,000,000
Subsequent Event \| $250 Million Unsecured Term Loan \| Unsecured Debt
Debt [Line Items]
Debt instrument, extension, term	1 year
Debt instrument face amount	$ 250,000,000