Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Shareholders' Equity (Details) $ / shares in Units, $ in Thousands				6 Months Ended
	Mar. 07, 2017 USD ($) $ / shares shares	May 09, 2016 USD ($)	Aug. 05, 2015 USD ($)	Jun. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares
Class of Stock [Line Items]
Preferred stock, par value (in usd per share) | $ / shares				$ 1		$ 1
Liquidation preference (per share) | $ / shares				$ 10,000		$ 10,000
Liquidation preference value				$ 137,500
Carrying Amount				$ 132,097		$ 132,097
Number of shares authorized to be repurchased | shares					950,000
Shares authorized to be repurchased | shares				747,494
Proceeds from common stock issued				$ 485,194	$ 0
Series B Depositary Shares
Class of Stock [Line Items]
Depository shares to preferred stock ratio			0.0025
Series B Preferred Stock
Class of Stock [Line Items]
Ownership per share			6.625%
Liquidation preference value			$ 80,000
Carrying Amount				76,812		76,812
Series C Depository Shares
Class of Stock [Line Items]
Depository shares to preferred stock ratio		0.0025
Series C Preferred Stock
Class of Stock [Line Items]
Ownership per share		6.60%
Liquidation preference value		$ 57,500
Carrying Amount				$ 55,285		$ 55,285
Common Stock
Class of Stock [Line Items]
Common stock issued (in shares) | shares	6,100,000
Price per share of stock of issued | $ / shares	$ 83.00
Proceeds from common stock issued	$ 485,200