Shareholders' Equity - Cash Dividends Declared (Details) - $ / shares	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Cash dividends declared, per common share (in dollars per share)	$ 0.31	$ 0.31	$ 0.31	$ 0.31	$ 0.81	$ 0.31	$ 0.31	$ 0.31	$ 5.00	$ 0.31	$ 0.31	$ 0.31	$ 1.24	$ 1.74	$ 5.93
Special Dividends
Class of Stock [Line Items]
Cash dividends declared, per common share (in dollars per share)					$ 0.50				$ 4.69