Shareholders' Equity (Shareholders' Equity Narrative) (Details)			12 Months Ended
	Feb. 16, 2018 USD ($) $ / shares	Oct. 13, 2017 shares	Dec. 31, 2019 USD ($) vote stock_class $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	May 20, 2019 shares	May 19, 2019 shares	Jul. 30, 2018 USD ($)	Sep. 06, 2011 USD ($)
Schedule of Shareholders' Equity Activity [Line Items]
Number of classes of common stock | stock_class			3
Preferred stock authorized (in shares)			500,000.0	500,000.0
Preferred stock, par value (in dollars per shares) | $ / shares			$ 0.01	$ 0.01
Preferred stock issued			0	0	0
Purchases of treasury stock | $				$ 36,700,000	$ 3,800,000
Share Price | $ / shares	$ 22.18
Employee stock ownership plan contribution | $	$ 22,300,000		$ 0	$ 22,300,000	$ 0
Capital stock, shares authorized						205,500,000	180,500,000
Treasury Stock
Schedule of Shareholders' Equity Activity [Line Items]
Number of shares repurchased				1,900,000	200,000
Purchases of treasury stock | $				$ 36,700,000	$ 3,800,000
Cancellation of class B treasury, shares					(1,200,000)
Common Class A
Schedule of Shareholders' Equity Activity [Line Items]
Number of votes per share | vote			1
Stock repurchase program, authorized amount | $								$ 100,000,000.0
Number of shares repurchased			0	1,871,631	200,605
Average cost per share (in dollars per share) | $ / shares				$ 19.59	$ 18.89
Purchases of treasury stock | $				$ 36,700,000
Remaining authorized repurchase amount | $			$ 100,000,000.0
Common stock, shares authorized			105,000,000.0	105,000,000		105,000,000.0	80,000,000.0
Common Class A | Treasury Stock
Schedule of Shareholders' Equity Activity [Line Items]
Stock repurchase program, authorized amount | $									$ 100,000,000.0
Common Class B
Schedule of Shareholders' Equity Activity [Line Items]
Number of votes per share | vote			10
Common stock, shares authorized			80,000,000.0	80,000,000
Common Class B | Treasury Stock
Schedule of Shareholders' Equity Activity [Line Items]
Cancellation of class B treasury, shares		1,027,907
Class B common stock converted (in shares)			0	284,845
Common Class C
Schedule of Shareholders' Equity Activity [Line Items]
Number of votes per share | vote			10
Common stock, shares authorized			20,000,000.0	20,000,000