Earnings per Share (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares
Earnings per share
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			380,000
Calculation of basic and diluted earnings per share
Net income (loss) | $	$ 3,114	$ 208,938	$ (107,452)	$ 334,325
Basic weighted-average common shares outstanding	67,961,000	67,379,000	67,638,000	67,169,000
Add: dilutive effect of stock options, unvested RSU's, and contingent PSU's	158,000	1,051,000	0	1,089,000
Diluted weighted-average common shares outstanding	68,119,000	68,430,000	67,638,000	68,258,000
Basic net income (loss) per common share | $ / shares	$ 0.05	$ 3.10	$ (1.59)	$ 4.98
Diluted net income (loss) per common share | $ / shares	$ 0.05	$ 3.05	$ (1.59)	$ 4.90
Performance Shares [Member]
Earnings per share
Share-based Compensation, Awards Other Than Options, Performance Measurement Period	3		3
Minimum [Member] | Performance Shares [Member]
Earnings per share
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit			0.00%
Maximum [Member] | Performance Shares [Member]
Earnings per share
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit			200.00%