Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended	9 Months Ended
	Sep. 23, 2019	Sep. 20, 2019	May 24, 2018	Sep. 30, 2019	Dec. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Treasury stock shares				800,000	900,000
Treasury stock, Cost basis				$ 14.9	$ 18.5
Common shares outstanding				90,822,000	85,643,000
2018 Stock Buyback Program [Member]
Equity, Class of Treasury Stock [Line Items]
Shares authorized for repurchase			5.00%
Number of shares authorized for repurchase	5,500,000		4,300,000
Common shares outstanding			85,300,000
Stock repurchase expiration date	Dec. 31, 2020		Dec. 31, 2019
Shares repurchased				200,000
Shares purchased price per share				$ 41.30
MidSouth [Member]
Equity, Class of Treasury Stock [Line Items]
Shares issued		5,000,000.0		5,000,000.0
Business combination, price per share		$ 38.42
Restricted Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares nonvested				1,300,000	1,300,000