Shareholders' Equity - Changes in Common Shares (Details) - $ / shares shares in Thousands	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
Dividends Payable [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
Common Stock Outstanding Rollforward [Roll Forward]
Beginning Balance (shares)				53,637				53,457				53,251	53,637	53,457	53,251
Shares issued due to vesting of share-based compensation awards (shares)													132	135	132
Other shares issued for compensation and shares reissued to stock purchase plan (shares)													23	45	74
Ending Balance (shares)	53,792				53,637				53,457				53,792	53,637	53,457
Special Dividends
Dividends Payable [Line Items]
Cash dividends declared, per common share (in dollars per share)					$ 0.50				$ 4.69