Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands														1 Months Ended		12 Months Ended
	Feb. 22, 2019	Jan. 15, 2019	Jan. 03, 2019	Nov. 06, 2018	Nov. 01, 2018	Oct. 02, 2018	Aug. 01, 2018	Jul. 27, 2018	Jul. 03, 2018	Jun. 06, 2018	Apr. 20, 2018	Apr. 03, 2018	Feb. 23, 2018	Jun. 30, 2018	May 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Shares
Authorized share capital																825,000,000
Common shares, shares authorized																800,000,000	800,000,000
Common shares, par value (in dollars per share)																$ 0.001	$ 0.001
Common shares, shares issued																409,652,000	367,510,000
Proceeds from issuance of common shares, net of issuance costs																$ 301,404	$ 8,300	$ 967
Shares repurchased																	3,100,000
Total aggregate amount of shares purchased																	$ 18,100
Treasury shares reissued during the year																0	0	0
Common stock dividend declared (in dollars per share)				$ 0.06				$ 0.06			$ 0.06		$ 0.06			$ 0.24		$ 0.24
Cash dividends paid						$ 21,400			$ 21,500			$ 19,100					$ 68,503	$ 50,924
Preferred shares, shares issued																5,750	5,750
Preferred stock, rate (as a percent)																6.00%	6.00%
Preferred stock, par value (in dollars per share)																$ 0.001	$ 0.001
Preferred stock, liquidation preference (in dollars per share)																$ 50	$ 50
Aggregate net proceeds																$ 277,927
Repurchase of treasury shares																	$ 18,071	$ 1,687
Preferred shares, shares authorized																25,000,000
Officers and Directors
Common Shares
Restricted stock awarded to executive officers, key employees & directors																4,460,592	1,989,915	3,919,696
Restricted shares awarded, average market price (in dollars per share)																$ 6.40	$ 13.08	$ 9.85
Mandatory Convertible Preferred Shares
Common Shares
Preferred shares, shares issued															5,750,000
Preferred stock, rate (as a percent)															6.00%
Preferred stock, par value (in dollars per share)															$ 0.001
Preferred stock, liquidation preference (in dollars per share)															$ 50
Cash dividend per mandatory convertible preferred shares				$ 0.75				$ 0.75		$ 0.64						$ 2.14
Mandatory Convertible Preferred Shares | Underwriters option
Common Shares
Preferred shares, shares issued															750,000
Common Shares
Common Shares
Common shares, shares issued															35,000,000
Share price of shares purchased (in dollars per share)															$ 7.75
Proceeds from issuance of common shares, net of issuance costs														$ 301,400
Number of consecutive trading days to calculate average share price of common stock															20 days
Common Shares | Underwriters option
Common Shares
Common shares, shares issued														5,250,000
Common Shares | Minimum
Common Shares
Conversion ratio															5.3763	5.5775
Common Shares | Maximum
Common Shares
Conversion ratio															6.4516	6.6931
Common Shares | Mandatory Convertible Preferred Shares | Underwriters option
Common Shares
Aggregate net proceeds															$ 277,900
Retained Earnings | Mandatory Convertible Preferred Shares
Common Shares
Cash dividends paid					$ 4,300		$ 3,700
Forecast
Common Shares
Common stock dividend declared (in dollars per share)	$ 0.01
Cash dividends paid			$ 21,000
Forecast | Mandatory Convertible Preferred Shares
Common Shares
Cash dividends paid		$ 4,300
Cash dividend per mandatory convertible preferred shares	$ 0.75