Summary of Significant Accounting Policies Earnings Per Share (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares		Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	256		0	0
Earnings Per Share Reconciliation [Abstract]
Net Income (loss) | $	$ (447,710)		$ 666,051	$ 170,935
Weighted Average Number of Shares Outstanding, Basic	67,723		67,230	66,615
Incremental Common Shares Attributable to Share-based Payment Arrangements	0	[1]	814	1,383
Weighted Average Number of Shares Outstanding, Diluted	67,723		68,044	67,998
Basic net income (loss) per common share | $ / shares	$ (6.61)		$ 9.91	$ 2.57
Diluted net income (loss) per common share | $ / shares	$ (6.61)		$ 9.79	$ 2.51
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	1.0		0.55	1.725
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

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