Benefit Plans (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension and Supplemental Executive Retirement Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost		$ 2,152	$ 1,876	$ 3,816	$ 3,697
Interest cost		2,779	3,336	5,589	6,750
Expected return on plan assets		(5,256)	(5,473)	(10,458)	(11,053)
Amortization of net actuarial losses (gains)		1,255	1,526	2,805	3,160
Amortization of prior service cost (credit)		(59)	(62)	(119)	(124)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total		871	1,203	1,633	2,430
Other Postretirement Benefit Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost		390	322	754	631
Interest cost		160	202	324	416
Expected return on plan assets		(2,216)	(1,852)	(4,431)	(3,704)
Amortization of net actuarial losses (gains)		(409)	(201)	(848)	(391)
Amortization of prior service cost (credit)		53	12	106	25
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total		$ (2,022)	$ (1,517)	$ (4,095)	$ (3,023)
Pension Plan | Subsequent Event
Components of Net Periodic Benefit Cost [Abstract]
Company contribution to pension plan	$ 6,800