Debt - $700 Million Revolving Credit Facility (Details) - Line of Credit [Member] - $700 Million Revolving Credit Facility [Member] - Revolving Credit Facility [Member]	12 Months Ended
	Dec. 31, 2018 USD ($)
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 700,000,000
Credit facility, maturity date	May 23, 2021
Additional borrowings	$ 0
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Spread rate (as a percent)	1.55%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread rate (as a percent)	1.55%
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread rate (as a percent)	2.40%