Employee Benefit Plans (Details 5) (USD $) In Thousands, unless otherwise specified				12 Months Ended														12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Limited partnership interests Significant unobservable inputs (Level 3)	Dec. 31, 2011 Limited partnership interests Significant unobservable inputs (Level 3)	Dec. 31, 2012 Defined benefit pension plan	Dec. 31, 2011 Defined benefit pension plan	Dec. 31, 2010 Defined benefit pension plan	Dec. 31, 2012 Defined benefit pension plan Forecast	Dec. 31, 2012 Defined benefit pension plan Recurring basis	Dec. 31, 2011 Defined benefit pension plan Recurring basis	Dec. 31, 2012 Defined benefit pension plan Recurring basis Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Defined benefit pension plan Recurring basis Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2012 Defined benefit pension plan Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Recurring basis Significant unobservable inputs (Level 3)	Dec. 31, 2011 Defined benefit pension plan Recurring basis Significant unobservable inputs (Level 3)	Dec. 31, 2012 Defined benefit pension plan Equity securities	Dec. 31, 2011 Defined benefit pension plan Equity securities	Dec. 31, 2012 Defined benefit pension plan Debt securities	Dec. 31, 2011 Defined benefit pension plan Debt securities	Dec. 31, 2012 Defined benefit pension plan Other	Dec. 31, 2011 Defined benefit pension plan Other	Dec. 31, 2012 Defined benefit pension plan Common collective trust funds Recurring basis	Dec. 31, 2011 Defined benefit pension plan Common collective trust funds Recurring basis	Dec. 31, 2012 Defined benefit pension plan Common collective trust funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Common collective trust funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Equity index funds Recurring basis	Dec. 31, 2011 Defined benefit pension plan Equity index funds Recurring basis	Dec. 31, 2012 Defined benefit pension plan Equity index funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Equity index funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Midcap index funds Recurring basis	Dec. 31, 2011 Defined benefit pension plan Midcap index funds Recurring basis	Dec. 31, 2012 Defined benefit pension plan Midcap index funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Midcap index funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan World equity index funds Recurring basis	Dec. 31, 2011 Defined benefit pension plan World equity index funds Recurring basis	Dec. 31, 2012 Defined benefit pension plan World equity index funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan World equity index funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan U.S. equity market funds Recurring basis	Dec. 31, 2011 Defined benefit pension plan U.S. equity market funds Recurring basis	Dec. 31, 2012 Defined benefit pension plan U.S. equity market funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan U.S. equity market funds Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Fixed maturities Recurring basis	Dec. 31, 2011 Defined benefit pension plan Fixed maturities Recurring basis	Dec. 31, 2012 Defined benefit pension plan Fixed maturities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Fixed maturities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan U.S. government direct obligations and U.S. agencies Recurring basis	Dec. 31, 2011 Defined benefit pension plan U.S. government direct obligations and U.S. agencies Recurring basis	Dec. 31, 2012 Defined benefit pension plan U.S. government direct obligations and U.S. agencies Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan U.S. government direct obligations and U.S. agencies Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Obligations of U.S. states and their subdivisions Recurring basis	Dec. 31, 2011 Defined benefit pension plan Obligations of U.S. states and their subdivisions Recurring basis	Dec. 31, 2012 Defined benefit pension plan Obligations of U.S. states and their subdivisions Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Obligations of U.S. states and their subdivisions Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Corporate debt securities Recurring basis	Dec. 31, 2011 Defined benefit pension plan Corporate debt securities Recurring basis	Dec. 31, 2012 Defined benefit pension plan Corporate debt securities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Corporate debt securities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Asset-backed securities Recurring basis	Dec. 31, 2011 Defined benefit pension plan Asset-backed securities Recurring basis	Dec. 31, 2012 Defined benefit pension plan Asset-backed securities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Asset-backed securities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Commercial mortgage-backed securities Recurring basis	Dec. 31, 2011 Defined benefit pension plan Commercial mortgage-backed securities Recurring basis	Dec. 31, 2012 Defined benefit pension plan Commercial mortgage-backed securities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2011 Defined benefit pension plan Commercial mortgage-backed securities Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Preferred stock Recurring basis	Dec. 31, 2011 Defined benefit pension plan Preferred stock Recurring basis	Dec. 31, 2012 Defined benefit pension plan Preferred stock Recurring basis Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Defined benefit pension plan Preferred stock Recurring basis Significant other observable inputs (Level 2)	Dec. 31, 2012 Defined benefit pension plan Limited partnership interests Recurring basis	Dec. 31, 2011 Defined benefit pension plan Limited partnership interests Recurring basis	Dec. 31, 2012 Defined benefit pension plan Limited partnership interests Recurring basis Significant unobservable inputs (Level 3)	Dec. 31, 2011 Defined benefit pension plan Limited partnership interests Recurring basis Significant unobservable inputs (Level 3)	Dec. 31, 2012 Defined benefit pension plan Money market funds Recurring basis	Dec. 31, 2011 Defined benefit pension plan Money market funds Recurring basis	Dec. 31, 2012 Defined benefit pension plan Money market funds Recurring basis Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Defined benefit pension plan Money market funds Recurring basis Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2012 Post-retirement medical plan Forecast	Dec. 31, 2012 Supplemental executive retirement plan Forecast
Details of investment out of defined benefit plan assets
Assets (as a percent)						100.00%	100.00%											56.00%	52.00%	41.00%	44.00%	3.00%	4.00%
Defined benefit plan assets	$ 336,534	$ 293,336	$ 282,616	$ 6,485	$ 7,116	$ 336,534	$ 293,336	$ 282,616		$ 336,534	$ 293,336	$ 3,343	$ 4,007	$ 326,706	$ 282,213	$ 6,485	$ 7,116							$ 188,411	$ 151,925	$ 188,411	$ 151,925	$ 60,601	$ 49,211	$ 60,601	$ 49,211	$ 60,289	$ 48,406	$ 60,289	$ 48,406	$ 6,798	$ 5,336	$ 6,798	$ 5,336	$ 60,723	$ 48,972	$ 60,723	$ 48,972	$ 138,295	$ 130,177	$ 138,295	$ 130,177	$ 9,907	$ 10,676	$ 9,907	$ 10,676	$ 16,899	$ 22,467	$ 16,899	$ 22,467	$ 100,142	$ 86,836	$ 100,142	$ 86,836	$ 8,386	$ 7,711	$ 8,386	$ 7,711	$ 2,961	$ 2,487	$ 2,961	$ 2,487	$ 134	$ 111	$ 134	$ 111	$ 6,485	$ 7,116	$ 6,485	$ 7,116	$ 3,209	$ 4,007	$ 3,209	$ 4,007
Additional information about assets of the Defined Benefit Retirement Plan measured at fair value on a recurring basis and for which the company has utilized Level 3 inputs to determine fair value
Value of plan assets at the beginning of the period	336,534	293,336	282,616	7,116	6,030	336,534	293,336	282,616		336,534	293,336	3,343	4,007	326,706	282,213	6,485	7,116							188,411	151,925	188,411	151,925	60,601	49,211	60,601	49,211	60,289	48,406	60,289	48,406	6,798	5,336	6,798	5,336	60,723	48,972	60,723	48,972	138,295	130,177	138,295	130,177	9,907	10,676	9,907	10,676	16,899	22,467	16,899	22,467	100,142	86,836	100,142	86,836	8,386	7,711	8,386	7,711	2,961	2,487	2,961	2,487	134	111	134	111	6,485	7,116	6,485	7,116	3,209	4,007	3,209	4,007
Purchases				61	(34)
Issuances				(692)	1,542
Settlements					(422)
Value of plan assets at the end of the period	336,534	293,336	282,616	6,485	7,116	336,534	293,336	282,616		336,534	293,336	3,343	4,007	326,706	282,213	6,485	7,116							188,411	151,925	188,411	151,925	60,601	49,211	60,601	49,211	60,289	48,406	60,289	48,406	6,798	5,336	6,798	5,336	60,723	48,972	60,723	48,972	138,295	130,177	138,295	130,177	9,907	10,676	9,907	10,676	16,899	22,467	16,899	22,467	100,142	86,836	100,142	86,836	8,386	7,711	8,386	7,711	2,961	2,487	2,961	2,487	134	111	134	111	6,485	7,116	6,485	7,116	3,209	4,007	3,209	4,007
Ranges of targets for the allocation of invested defined benefit plan assets
Targets for the allocation of invested defined benefit plan assets, minimum (as a percent)																		25.00%		25.00%		0.00%
Targets for the allocation of invested defined benefit plan assets, maximum (as a percent)																		80.00%		75.00%		40.00%
Expected payments
Expected employer contribution to the plan for the next fiscal year									$ 6,300																																																																							$ 637	$ 3,720