Shareholders' Equity (Narrative) (Details) - USD ($)			12 Months Ended
	Jun. 01, 2015	Dec. 04, 2012	Dec. 31, 2017	Dec. 31, 2016	Dec. 06, 2012	Jun. 08, 2011
Class of Stock [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			28,690			3,282,276
Common stock par value (in usd per share)			$ 0.01	$ 0.01		$ 0.01
Exercise price of warrants or rights (in usd per share)						$ 18.28
Warrants exercised in cashless exchange			44,275
Warrants outstanding (in shares)			8,752
Preferred Stock, Par or Stated Value Per Share			$ 0.01	$ 0.01
Conversion price (in usd per share)	$ 25,400
Common Stock [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 100,000,000
Treasury stock acquired, average cost per share (in usd per share)			$ 52.18
Stock repurchase program, remaining authorized repurchase amount			$ 103,900,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			28,690
Series A [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percent)	6.40%
Preferred Stock, Par or Stated Value Per Share	$ 0.01
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percent)		5.25%
Preferred Stock, Par or Stated Value Per Share		$ 0.01
Preferred stock, liquidation preference per share (in usd per share)		$ 25,000
Depository shares, issued		6,000,000
Depository share, par or stated value per share (in usd per share)		$ 25