Shareholders' Equity - Stock Buyback Program (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Apr. 30, 2018	Feb. 14, 2018
Equity, Class of Treasury Stock [Line Items]
Purchase of treasury shares	$ 95,175,000
Common Stock | February 2018 Stock Buyback Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount			$ 200,000,000
Purchase of treasury shares (in shares)	4,210,254
Purchase of treasury shares	$ 95,200,000
Line of Credit | Revolving Credit Facility | Amended Credit Agreement
Equity, Class of Treasury Stock [Line Items]
Maximum borrowing capacity		$ 900,000,000