Shareholders' Equity (Details) - USD ($)							1 Months Ended	12 Months Ended
	Feb. 03, 2017	Oct. 16, 2013	Oct. 11, 2013	Oct. 30, 2008	Jul. 03, 2008	Jun. 15, 2007	Feb. 28, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2010
Stockholders' Equity
Amount of common stock authorized to repurchase	$ 100,000,000
Period of stock repurchase period	2 years
Number of shares of common stock repurchased								1,264,149
Amount for which shares of stock are repurchased								$ 24,800,000
Average price paid per share of common stock repurchased (in dollars per share)								$ 19.59
Preferred equity investment
Consideration that the shareholders would have received under merger agreement before termination (in dollars per share)						$ 67.00
Total consideration from the termination of the Merger Agreement					$ 1,475,000,000
Non-refundable cash termination fee from the termination of the Merger Agreement					225,000,000
Investment in preferred equity from the termination of the Merger Agreement					$ 1,250,000,000
Repurchase value of preferred stock								$ 24,796,000
Affiliates Of Fortress Centerbridge And W F Investment Holdings
Preferred equity investment
Exchange agreement amount paid			$ 649,500,000
Maximum | Affiliate of Fortress Investment Group LLC
Preferred equity investment
Ownership interest in Spin-Off entity (as a percent)		9.90%
Common Stock | Affiliate of Fortress Investment Group LLC
Changes in each class of the Company's Preferred Stock
Conversion of preferred stock (in shares)									8,624,000
Series B Preferred Stock
Preferred equity investment
Issuance of preferred stock (in shares)				12,500
Repurchase value of preferred stock										$ 11,200,000
Number of shares held								0	0
Changes in each class of the Company's Preferred Stock
Shares outstanding at the beginning of the period								0	0
Repurchase of Preferred Stock (in shares)			2,300							225
Shares outstanding at the end of the period								0	0
Series B Preferred Stock | Wells Fargo Investment Holdings LLC
Changes in each class of the Company's Preferred Stock
Repurchase of Preferred Stock (in shares)							225
Series B Preferred Stock | Affiliate of Fortress Investment Group LLC
Preferred equity investment
Number of shares of preferred stock provided with the right to exchange as per the Exchange Agreement		9,750
Ceiling price at which the shares of preferred stock are redeemable at maturity (in dollars per share)		$ 67
Series C Preferred Stock
Preferred equity investment
Number of shares held								0	0
Changes in each class of the Company's Preferred Stock
Shares outstanding at the beginning of the period								0
Shares outstanding at the end of the period								0	0
Number of shares converted									8,624
Conversion of preferred stock (in shares)									8,624,000
Series C Preferred Stock | Affiliate of Fortress Investment Group LLC
Preferred equity investment
Issuance of preferred stock (in shares)			14,553
Repurchase price of preferred stock (in dollars per share)		$ 67
Changes in each class of the Company's Preferred Stock
Repurchase of Preferred Stock (in shares)			5,929
Series C Preferred Stock | Affiliate of Fortress Investment Group LLC
Preferred equity investment
Number of shares held									8,624
Changes in each class of the Company's Preferred Stock
Shares outstanding at the beginning of the period									8,624
Number of shares converted									8,624