Shareholders' Equity and Other Comprehensive Income (Narrative) (Details) - USD ($)			3 Months Ended		12 Months Ended
	Aug. 01, 2018	Jun. 21, 2018	Jun. 30, 2018	Sep. 30, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Proceeds from issuance of stock					$ 195,140,000	$ 0	$ 0
Repurchases of common stock					$ 175,072,000	175,079,000	$ 263,084,000
Repurchase of common stock					3,653,000
Stock repurchase program, authorized amount					$ 150,000,000	$ 200,000,000
Warrant outstanding (in shares)					0	2,200,000.0	2,200,000.0
Warrant, exercise price (per share)					$ 0	$ 65.52	$ 65.52
Fourth Quarter of 2017
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 25,000,000
Repurchase of Common Stock 300 Million
Class of Stock [Line Items]
Stock repurchase program, authorized amount							$ 300,000,000
Stock repurchase program, period in force				15 months
Series D Preferred Stock
Class of Stock [Line Items]
Cash dividends paid					6,300,000
Proceeds from issuance of stock		$ 200,000,000
Series C Preferred Stock
Class of Stock [Line Items]
Redemption price per share (in dollars per share)	$ 25.00
Cash dividends paid	$ 2,600,000				7,678,000	$ 10,238,000	10,238,000
Repurchases of common stock					130,000,000
Preferred Stock | Series C Preferred Stock
Class of Stock [Line Items]
Stock redeemed or called during period (in shares)	5,200,000
Stock redeemed or called during period	$ 130,000,000
Dividends			$ 4,000,000
Redemption period from regulatory capital treatment		90 days
Repurchases of common stock					125,980,000
Sale of Stock, Price Per Share		$ 25.00
Consideration received on transaction		$ 195,100,000
Preferred Stock | Series C Preferred Stock | Till June 20, 2023
Class of Stock [Line Items]
Dividend rate, percentage		6.30%
Preferred Stock | Series C Preferred Stock | From June 21, 2023 | LIBOR
Class of Stock [Line Items]
Dividend rate, percentage		3.352%
Treasury Stock
Class of Stock [Line Items]
Repurchases of common stock					175,072,000	$ 175,079,000	$ 263,084,000
Repurchase of common stock						4,021,000	8,715,000
Common Stock
Class of Stock [Line Items]
Repurchases of common stock					$ 175,000,000	$ 175,000,000	$ 262,900,000
Common Stock | Open Market Transactions
Class of Stock [Line Items]
Stock repurchase program, repurchased amount							$ 212,900,000
Stock repurchase program, shares repurchased							7,300,000
Common Stock | Accelerated Share Repurchase Program
Class of Stock [Line Items]
Stock repurchase program, repurchased amount							$ 50,000,000
Stock repurchase program, shares repurchased							1,400,000