Net income (loss) per share - (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net income (loss) (numerator):
Income (loss) from continuing operations—basic and diluted	$ (18,899)	$ 35,294	$ (19,112)	$ 36,431
Income from discontinued operations, net of tax—basic and diluted	0	518	0	790
Net income (loss)—basic and diluted	$ (18,899)	$ 35,812	$ (19,112)	$ 37,221
Weighted average shares (denominator):
Weighted average shares-basic (in shares)	141,298	127,362	141,183	127,281
Non-vested restricted stock (in shares)	0	2,022	0	1,838
Weighted average shares-diluted (in shares)	141,298	129,384	141,183	129,119
Net income (loss) per share:
Income (loss) from continuing operations, per basic share	$ (0.13)	$ 0.28	$ (0.14)	$ 0.29
Income from discontinued operations, net of tax, per basic share	$ 0.00	$ 0.00	$ 0.00	$ 0.01
Basic (in dollars per share)	$ (0.13)	$ 0.28	$ (0.14)	$ 0.30
Income from continuing operations, per diluted share	$ (0.13)	$ 0.27	$ (0.14)	$ 0.28
Income from discontinued operations, net of tax, per diluted share	$ 0.00	$ 0.00	$ 0.00	$ 0.01
Diluted (in dollars per share)	$ (0.13)	$ 0.27	$ (0.14)	$ 0.29