Fair Value Measurements - Narrative (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
$400 Million 5% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Face amount	$ 400,000,000.0
Senior Notes [Member] | $400 Million 5% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Face amount	$ 400,000,000
Stated interest rate (as a percent)	5.00%
Debt amount	$ 397,469,000	$ 396,778,000
Fair value of notes	390,300,000
Senior Notes [Member] | $700 Million 4.75% Senior Note [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Face amount	$ 700,000,000
Stated interest rate (as a percent)	4.75%
Debt amount	$ 691,200,000
Fair value of notes	$ 644,700,000