Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Mar. 01, 2018	Oct. 16, 2017	Sep. 14, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Preferred Stock Information
Preferred stock, value outstanding				$ 169,302	$ 265,821
Preferred stock, par value (in dollars per share)				$ 0.01	$ 0.01
Preferred stock, value issued				$ 169,302	$ 265,821
Series C non-cumulative perpetual preferred stock
Preferred Stock Information
Preferred stock, value outstanding				$ 169,302	$ 169,302
Preferred stock, depositary shares outstanding				7,000,000	7,000,000
Annual rate of dividend (as a percent)				5.70%	5.70%
Preferred stock, par value (in dollars per share)				$ 0.01	$ 0.01
Preferred stock, liquidation preference per share				25,000	25,000
Preferred stock, liquidation preference per depositary share				$ 25	$ 25
Preferred stock, value issued			$ 175,000
Deferred stock issuance costs of preferred stock			5,700
Net proceeds of the offering, after deducting stock issuance costs			$ 169,300
Series B non-cumulative perpetual preferred stock
Preferred Stock Information
Preferred stock, value outstanding				$ 0	$ 96,519
Annual rate of dividend (as a percent)	6.45%			6.45%	6.45%	6.45%
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, liquidation preference per share	$ 25
Deferred stock issuance costs of preferred stock	$ 3,500
Redemption of Preferred Stock (in shares)	4,000,000
Redemption of Preferred Stock	$ 100,000			$ 100,000
Series A non-cumulative perpetual preferred stock
Preferred Stock Information
Annual rate of dividend (as a percent)		7.50%			7.50%	7.50%
Preferred stock, par value (in dollars per share)		$ 0.01
Preferred stock, liquidation preference per share		25,000
Preferred stock, liquidation preference per depositary share		$ 25
Deferred stock issuance costs of preferred stock		$ 5,800
Redemption of Preferred Stock (in shares)		6,900,000
Redemption of Preferred Stock		$ 172,500			$ 172,500