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Earnings (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net loss	$ (58,273)	$ (56,112)	$ (83,951)	$ (16,230)
Amount allocated to common stockholders (in hundredths)	100.00%	100.00%	100.00%	100.00%
Basic EPS:
Net loss allocated to common stockholders	$ (58,273)	$ (56,112)	$ (83,951)	$ (16,230)
Net loss allocated to common stockholders (shares)	87,076,000	86,907,000	87,059,000	87,524,000
Net loss allocated to common stockholders (in dollars per share)	$ (0.67)	$ (0.65)	$ (0.96)	$ (0.19)
Stock options [Member]
Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (shares)	372,569	317,266	391,375	327,599
Service-based share awards [Member]
Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted EPS (shares)	1,449,520	646,128	1,157,077	599,001

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Percentage of net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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