Employee Benefit Plans (Details) $ in Thousands			12 Months Ended
	May 05, 2004 yr	Jan. 01, 1997 week	Dec. 31, 2017 USD ($) yr shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Recognized stock compensation expense			$ 13,300	$ 9,600	$ 15,300
Deferred compensation plan			$ 5,390	$ 4,578
Employee Thrift Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution of shares, common stock | shares			155,822	630,039	235,104
Recognized stock compensation expense			$ 4,400	$ 4,000	$ 6,200
Separation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service period, years		20 years
Maximum period benefit, weeks | week		104
Separation benefit plans expense			$ 2,700	$ 3,100	$ 3,000
Special Separation Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service period, years	20 years
Age limit | yr	65
Change Of Control Contracts [Member]
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
Plan401k [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional period for 401k, years			3 years