Summary of Significant Accounting Policies Earnings Per Share (Details) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2016 USD ($) $ / shares shares		Dec. 31, 2015 USD ($) $ / shares shares		Dec. 31, 2014 USD ($) $ / shares shares	Aug. 12, 2016 USD ($)
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Capped Call, Cap Price | $ / shares		$ 60.00
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		280		256		0
Earnings Per Share Reconciliation [Abstract]
Net Income (loss) | $		$ (757,744)		$ (447,710)		$ 666,051
Weighted Average Number of Shares Outstanding, Basic		76,568		67,723		67,230
Incremental Common Shares Attributable to Share-based Payment Arrangements	[1]	0		0		814
Incremental Common Shares Attributable to Conversion of Debt Securities, Treasury Stock Method		0	[2]	0	[2]	0
Weighted Average Number of Shares Outstanding, Diluted		76,568		67,723		68,044
Basic net income (loss) per common share | $ / shares		$ (9.90)		$ (6.61)		$ 9.91
Diluted net income (loss) per common share | $ / shares		$ (9.90)		$ (6.61)		$ 9.79
Performance Shares [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Award Vesting Period		3 years
Multiplier Applied to PSU Awards at Settlement		0.2		1.0		0.55
Minimum [Member] | Performance Shares [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Multiplier Applied to PSU Awards at Settlement		0
Maximum [Member] | Performance Shares [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Multiplier Applied to PSU Awards at Settlement		2
Convertible Debt [Member] | 1.50% Senior Convertible Notes Due 2021 [Domain]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Debt Instrument, Face Amount | $		$ 172,500		$ 0			$ 172,500
Debt Instrument, Convertible, Conversion Price | $ / shares		$ 40.50

[1] For the years ended December 31, 2016, and 2015, the shares were anti-dilutive and excluded from the calculation of diluted earnings per share.

[2] For the year ended December 31, 2016, shares of the Company’s common stock traded at an average closing price below the $40.50 conversion price, and therefore, had no dilutive impact and were excluded from the calculation of diluted earnings per share.