Share-Based Payments - Shares Issued Under Employee Stock Purchase Plan (Details) - USD ($) shares in Thousands, $ in Millions	1 Months Ended	12 Months Ended
Jun. 30, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under the 2015 ESPP (in shares)	6,200
2015 ESPP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares issued under the 2015 ESPP (in shares)		212	204	170
Cash received under the 2015 ESPP		$ 48.6	$ 40.4	$ 40.5

Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 505
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-Section S99
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration