Fair Value Measurements Fair Value of Financial Instrument Assumptions (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Fair Value of Financial Instrument Assumptions [Line Items]
Letters of Credit Potential Commitments, Amount	$ 65.6	$ 52.7
Revolving Credit Facility [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 500.0
Line of Credit Facility, Initiation Date	Jul. 18, 2013
Basis point spread on variable rate under Credit Facility	2.50%
Warehousing Agreement - Third Amendment to Second Amended and Restated [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 125.0
Line of Credit Facility, Initiation Date	Jun. 24, 2016
Basis point spread on variable rate under Credit Facility	2.00%
Repurchase Agreement - First Amendment to Second Amended and Restated [Member]
Fair Value of Financial Instrument Assumptions [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 50.0
Line of Credit Facility, Initiation Date	Oct. 30, 2017

[Line Items] for Fair Value of Financial Instrument Assumptions [Table]

No definition available.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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- Definition

Date the credit facility first became available, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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