Shareholders' Equity Common Stock Repurchase Plans (Details) - USD ($)	1 Months Ended			6 Months Ended	12 Months Ended
	Nov. 30, 2016	Apr. 30, 2015	Nov. 30, 2014	Apr. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity, Class of Treasury Stock [Line Items]
Common stock repurchase amount					$ 18,545,000	$ 50,000,000	$ 175,255,000
Acquisition of treasury stock					(18,545,000)	(50,000,000)	$ (175,255,000)
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchase amount						$ 95,200,000
Average cost per share of treasury stock acquired (usd per share)						$ 11.91
Acquisition of treasury stock (in shares)						(8,000,000.0)
Common Stock | Accelerated Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Treasury stock, value			$ 100,000,000
Common stock repurchase amount		$ 100,000,000.0
Average cost per share of treasury stock acquired (usd per share)				$ 12.05
Acquisition of treasury stock			$ (100,000,000)
Acquisition of treasury stock (in shares)		(1,800,000.0)	(6,500,000.0)	(8,300,000.0)
Percent of common shares outstanding, expected to be delivered			80.00%
Common Stock | April 2015 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Treasury stock, value		$ 50,000,000.0		$ 50,000,000.0
Common stock repurchase amount						$ 50,000,000.0
Average cost per share of treasury stock acquired (usd per share)						$ 12.57
Acquisition of treasury stock (in shares)						(4,000,000)
Percent of common shares outstanding, expected to be delivered		2.30%
Common Stock | November 2016 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Treasury stock, value	$ 50,000,000.0
Common stock repurchase amount					$ 18,500,000.0
Average cost per share of treasury stock acquired (usd per share)					$ 12.48
Remaining repurchase amount					$ 31,500,000.0
Acquisition of treasury stock (in shares)					(1,500,000)
Percent of common shares outstanding, expected to be delivered	2.30%