Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands													1 Months Ended		9 Months Ended		12 Months Ended
	Jan. 15, 2019	Nov. 06, 2018	Nov. 05, 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	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Common Shares
Common shares, shares issued															410,160,000		367,510,000
Proceeds from issuance of common shares, net of issuance costs													$ 21,800		$ 301,835	$ 8,300
Shares repurchased																	3,100,000
Total aggregate amount of shares purchased																	$ 18,100
Common stock dividend declared (in dollars per share)		$ 0.06					$ 0.06			$ 0.06		$ 0.06			$ 0.18	$ 0.18
Cash dividends paid					$ 21,400			$ 21,500			$ 19,100				$ 57,661	$ 51,346
Preferred shares, shares issued															5,750,000		5,750,000
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															$ 278,358
Cash dividend per mandatory convertible preferred shares															$ 1.39
Mandatory Convertible Preferred Shares
Common Shares
Preferred shares, shares issued														5,750,000,000
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
Mandatory Convertible Preferred Shares | Underwriters option
Common Shares
Preferred shares, shares issued														750,000
Common Shares
Common Shares
Common shares, shares issued														35,000,000,000
Share price of shares purchased (in dollars per share)														$ 7.75
Proceeds from issuance of common shares, net of issuance costs													$ 301,800
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													5,250,000,000
Common Shares | Minimum
Common Shares
Conversion ratio					5.4735									5.3763
Common Shares | Maximum
Common Shares
Conversion ratio					6.5683									6.4516
Common Shares | Mandatory Convertible Preferred Shares | Underwriters option
Common Shares
Aggregate net proceeds														$ 278,400
Retained Earnings | Mandatory Convertible Preferred Shares
Common Shares
Cash dividends paid				$ 4,300		$ 3,700
Forecast | Mandatory Convertible Preferred Shares
Common Shares
Cash dividends paid	$ 4,300