Earnings per share - Schedule of Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income (loss)	$ 16,821	$ (10,530)	$ 38,638	$ 17,109
Non-cash dividend to warrant holders	0	(879)	0	(879)
Preferred Share dividends	0	0	0	(7,922)
Allocation of undistributed earnings to preferred shareholders	0	0	0	(1,359)
Numerator for basic EPS - income (loss) available to ordinary shareholders	16,821	(11,409)	38,638	6,949
Add back Preferred Share dividends	0	0	0	0
Add back undistributed earnings to preferred shareholders	0	0	0	0
Numerator for diluted EPS - income (loss) available to ordinary shareholders after assumed conversions	$ 16,821	$ (11,409)	$ 38,638	$ 6,949
Denominator:
Denominator for basic EPS - weighted-average shares (in shares)	116,987,887	104,064,220	113,685,219	83,275,443
Effect of dilutive securities:
Unvested restricted share awards (in shares)	337,336	0	296,544	14,441
Preferred Shares (in shares)	0	0	0	0
Denominator for diluted EPS - adjusted weighted-average shares (in shares)	117,325,223	104,064,220	113,981,763	83,289,884
EPS - Basic (in dollars per share)	$ 0.14	$ (0.11)	$ 0.34	$ 0.08
EPS - Diluted (in dollars per share)	$ 0.14	$ (0.11)	$ 0.34	$ 0.08
Earnout Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares of common stock acquired by outstanding warrants (in shares)	3,000,000	3,000,000	3,000,000	3,000,000
Convertible Preferred Securities
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings (losses) per share (in shares)				15,927,778
Restricted Share Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings (losses) per share (in shares)		1,400,386
Unvested Performance-Based Equity Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings (losses) per share (in shares)	538,951	265,222	538,951	265,222