Debt - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Letters of credit outstanding expiring in current fiscal year	$ 29.1
Derivative liability	4.6
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 400.0
Line of credit facility, unused commitment fee percent	0.20%
Borrowings under Revolving Credit Facility	$ 100.0	$ 180.0
Line of credit facility, remaining borrowing capacity	253.8
Unamortized debt issuance expense	1.3
Letter of Credit | Line of Credit
Debt Instrument [Line Items]
Letters of credit outstanding, amount	$ 46.2
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
LIBOR variable rate spread	1.25%
Designated as Hedging Instrument | Interest Rate Swap
Debt Instrument [Line Items]
Derivative, notional amount	$ 100.0
Derivative, fixed interest rate	2.71%