Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income (loss)	$ 27,115	$ (14,066)	$ 2,954	$ (25,039)	$ 13,049	$ (22,085)
Less: Earnings allocated to unvested restricted stock awards	22		7		12	0
Earnings (loss) allocated to common shareholders	$ 27,093		$ 2,947		$ 13,037	$ (22,085)
Common stock:
Weighted average basic shares outstanding (in shares)	65,093		64,142		64,948	64,073
Effect of dilutive securities (in shares)	2,098		322		2,510	0
Weighted average diluted shares outstanding (in shares)	67,191		64,464		67,458	64,073
Basic earnings (loss) per share:
Net income (loss) (in dollars per share)	$ 0.42		$ 0.05		$ 0.20	$ (0.34)
Diluted earnings (loss) per share:
Net income (loss) (in dollars per share)	$ 0.40		$ 0.05		$ 0.19	$ (0.34)