Employee Benefit Plans, Changes in Fair Value of Plan Assets and Plan Benefit Obligations and Summary of Funded Status (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
Change in Fair Value of Plan Assets [Abstract]
Balance at end of year	$ 66,137,000		$ 62,105,000
Defined Benefit Pension Plan and Benefit Equalization Plan [Member]
Change in Fair Value of Plan Assets [Abstract]
Balance at beginning of year	62,105,000		61,702,000
Actual return on plan assets	3,621,000		(626,000)
Company contribution	5,780,000		6,234,000
Benefit payments	(5,369,000)		(5,205,000)
Balance at end of year	66,137,000		62,105,000		61,702,000
Change in Benefit Obligations [Abstract]
Balance at beginning of year	100,656,000		88,146,000
Interest cost	4,011,000		4,526,000		4,531,000
Assumption change loss	6,031,000		11,431,000
Actuarial (gain) loss	(9,000)		1,758,000
Benefit payments	(5,369,000)		(5,205,000)
Balance at end of year	105,320,000		100,656,000		88,146,000
Funded Status [Abstract]
Funded status at end of year	(39,183,000)		(38,551,000)
Amounts recognized in Consolidated Balance Sheets consist of:
Current liabilities	(187,000)		(264,000)
Long-term liabilities	(38,996,000)		(38,287,000)
Net amount recognized in Consolidated Balance Sheets	(39,183,000)		(38,551,000)
Amounts not yet reflected in net periodic benefit cost and included in accumulated other comprehensive loss:
Net actuarial loss	(60,935,000)		(59,239,000)
Accumulated other comprehensive loss	(60,935,000)		(59,239,000)			(39,500,000)
Cumulative Company contributions in excess of net periodic benefit cost	21,752,000		20,688,000
Net amount recognized in Consolidated Balance Sheets	(39,183,000)		(38,551,000)
Other comprehensive loss	1,700,000		14,800,000		4,900,000
Amount to be amortized from other comprehensive loss into cost in 2013	$ 6,300,000
Actuarial assumptions used to determine benefit obligation [Abstract]
Discount rate (in hundredths)	3.58%		4.10%
Rate of increase in compensation (in hundredths)		[1]		[1]
Measurement date	December 31		December 31
Expected return on assets (in hundredths)	7.00%		7.50%		7.50%
Expected return on assets in 2013 (in hundredths)	6.75%

[1] n.a.