Stockholders' Equity (Details Textuals)				1 Months Ended	12 Months Ended			45 Months Ended
	Sep. 15, 2016 USD ($) $ / shares shares	Jun. 15, 2015 $ / shares shares	Sep. 14, 2011 $ / shares shares	Nov. 30, 2008 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) shares	Sep. 15, 2021	Jul. 25, 2017 USD ($)	Aug. 28, 2015 USD ($)	Jul. 23, 2013 USD ($)	Dec. 06, 2011 $ / shares
Stockholders' Equity Note [Abstract]
Subsidiary equity balance | $					$ 3,300,000,000
Class of Stock [Line Items]
Common shares, par value (in usd per share) | $ / shares					$ 0.01	$ 0.01
Purchase of preferred stock | $						$ 1,248,000	$ 1,335,000
Series B Preferred Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount | $											$ 10,000,000
Treasury stock shares acquired (in shares) | shares							50,000
Preferred Stock, Dividend Rate, Percentage			8.00%
Depositary shares issued (in shares) | shares			2,600,000
Depository share ratio			0.025
Purchase of preferred stock | $	$ 59,000,000						$ 1,000,000
Liquidation preference on depositary shares (in usd per share) | $ / shares			$ 1,000
Series C Preferred Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount | $										$ 10,000,000
Remaining authorized repurchase amount | $					$ 10,000,000
Preferred Stock, Dividend Rate, Percentage		6.125%
Depositary shares issued (in shares) | shares		2,600,000
Depository share ratio		0.025
Preferred Stock, Dividend Payment Terms		Jun. 15, 2020
Redemption Price On Depositary Shares | $ / shares		$ 1,000
Liquidation preference on depositary shares (in usd per share) | $ / shares		1,000
Depositary share value (in usd per share) | $ / shares		$ 25
Series D Preferred Stock
Class of Stock [Line Items]
Stock repurchase program authorized amount | $									$ 15,000,000
Remaining authorized repurchase amount | $					$ 15,000,000
Preferred Stock, Dividend Rate, Percentage	5.375%
Depositary shares issued (in shares) | shares	4,000,000
Depository share ratio	0.025
Preferred Stock, Dividend Payment Terms								Sep. 15, 2021
Redemption Price On Depositary Shares | $ / shares	$ 1,000
Liquidation preference on depositary shares (in usd per share) | $ / shares	1,000
Depositary share value (in usd per share) | $ / shares	$ 25
Common Stock
Class of Stock [Line Items]
Treasury stock shares acquired (in shares) | shares					1,600,000	1,000,000
Warrants to purchase shares of common stock (in shares) | $				$ 4,000,000
Term of warrants				10 years
Exercise price of warrants (in usd per share) | $ / shares				$ 19.77
Common shares, par value (in usd per share) | $ / shares												$ 0.01
Treasury stock carrying basis | $					$ 37,000,000	$ 20,000,000
Treasury stock acquired average cost per share (in usd per share) | $ / shares					$ 23.59	$ 17.10
Repurchased amount for minimum tax withholding settlement | $					$ 9,000,000	$ 5,000,000
Repurchased shares for minimum tax withholding settlements (in shares) | shares					370,000	293,000
Minimum tax withholding settlement average cost per share (in usd per share) | $ / shares					$ 25.08	$ 17.30
Remaining authorized repurchase amount | $					$ 51,000,000