Earnings per Share (Details) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 12, 2016 shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)
Earnings per share
Stock Issued During Period, Shares, New Issues	18,400
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		506	0	193	380
Debt Instrument, Face Amount | $		$ 2,803,736		$ 2,803,736		$ 2,350,000
Capped Call, Cap Price | $ / shares		$ 60.00		$ 60.00
Calculation of basic and diluted earnings per share
Net income (loss) | $		$ (40,907)	$ 3,114	$ (556,798)	$ (107,452)
Basic weighted-average common shares outstanding		78,468	67,961	71,574	67,638
Add: dilutive effect of stock options, unvested RSU's, and contingent PSU's		0	158	0	0
Diluted weighted-average common shares outstanding		78,468	68,119	71,574	67,638
Basic net income (loss) per common share | $ / shares		$ (0.52)	$ 0.05	$ (7.78)	$ (1.59)
Diluted net income (loss) per common share | $ / shares		$ (0.52)	$ 0.05	$ (7.78)	$ (1.59)
Performance Shares [Member]
Earnings per share
Share-based Compensation, Awards Other Than Options, Performance Measurement Period				3 years
Multiplier Applied to PSU Awards at Settlement				0.2
Minimum [Member] | Performance Shares [Member]
Earnings per share
Multiplier Applied to PSU Awards at Settlement				0
Maximum [Member] | Performance Shares [Member]
Earnings per share
Multiplier Applied to PSU Awards at Settlement				2.00
1.50% Senior Convertible Notes Due 2021 [Domain]
Earnings per share
Debt Instrument, Face Amount | $		$ 172,500		$ 172,500		$ 0
Convertible Debt [Member] | 1.50% Senior Convertible Notes Due 2021 [Domain]
Earnings per share
Debt Instrument, Face Amount | $		$ 172,500		$ 172,500
Debt Instrument, Convertible, Conversion Price | $ / shares		$ 40.50		$ 40.50