Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Noncurrent liabilities	$ (159,582)	$ (140,623)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Rollforward]
Projected benefit obligation at beginning of year	413,147	346,464
Service cost	8,407	6,782	6,196
Interest cost	17,284	18,087	17,740
Actuarial loss	32,666	58,208
Plan amendments	0	0
Employee contributions	0	0
Benefits paid	(17,034)	(16,394)
Projected benefit obligation at end of year	454,470	413,147	346,464
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	295,655	302,464
Actual return on plan assets	41,729	8,977
Employer contributions	1,565	1,552
Employee contributions	0	0
Benefits paid	(17,034)	(16,394)
Other expense	(1,216)	(944)
Fair value of plan assets at end of year	320,699	295,655	302,464
Defined Benefit Plan, Funded Status of Plan [Abstract]
Funded status at end of year, net accrued benefit cost	(133,771)	(117,492)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Current liabilities	(1,702)	(1,626)
Noncurrent liabilities	(132,069)	(115,866)
Net amount recognized	(133,771)	(117,492)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Rollforward]
Projected benefit obligation at beginning of year	24,833	21,158
Service cost	918	673	587
Interest cost	956	972	1,029
Actuarial loss	2,021	3,934
Plan amendments	0	(631)
Employee contributions	1,136	1,609
Benefits paid	(2,282)	(2,882)
Projected benefit obligation at end of year	27,582	24,833	21,158
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	1,146	1,273
Employee contributions	1,136	1,609
Benefits paid	(2,282)	(2,882)
Other expense	0	0
Fair value of plan assets at end of year	0	0	0
Defined Benefit Plan, Funded Status of Plan [Abstract]
Funded status at end of year, net accrued benefit cost	(27,582)	(24,833)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Current liabilities	(1,256)	(1,262)
Noncurrent liabilities	(26,326)	(23,571)
Net amount recognized	$ (27,582)	$ (24,833)