Employee Benefit Plans (Details) $ in Thousands			12 Months Ended
	May 05, 2004 yr	Jan. 01, 1997 week	Dec. 31, 2016 USD ($) yr shares	Dec. 31, 2015 USD ($) shares		Dec. 31, 2014 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Recognized stock compensation expense			$ 9,600	$ 15,300	[1]	$ 17,400
Deferred compensation plan			$ 4,578	$ 4,244
Employee Thrift Plan
Defined Benefit Plan Disclosure [Line Items]
Contribution of shares, common stock | shares			630,039	235,104		120,333
Recognized stock compensation expense			$ 4,000	$ 6,200		$ 5,200
Separation Plan
Defined Benefit Plan Disclosure [Line Items]
Service period, years		20 years
Maximum period benefit, weeks | week		104
Separation benefit plans expense			$ 3,100	$ 3,000		$ 2,700
Special Separation Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Service period, years	20 years
Age limit | yr	65
Change Of Control Contracts
Defined Benefit Plan Disclosure [Line Items]
Employee contract period, years | yr			3
Employment contract period extension, years			1 year
Grace period following the first anniversary			30 days
Multiple for determination compensation			2.9
Plan 401k
Defined Benefit Plan Disclosure [Line Items]
Additional period for 401k, years			3 years

[1] In 2015, recognized stock compensation was reduced by $3.2 million, capitalized stock compensation cost for our oil and natural gas properties was reduced by $0.2 million, and the tax benefit was reduced by $1.2 million for lower expected payouts related to the performance shares.