Benefit Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 17, 2009
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer		$ 0	$ 0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ 28,551,000	$ (16,413,000)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.53%	4.60%	3.89%
Expected long-term rate of return on plan assets		7.00%
Accumulated benefit obligation for the pension plan		$ 129,300,000	$ 104,900,000
Common share purchased under pension plan, shares					115,800
Common share purchased under pension plan, value					$ 7,000,000.0
Common share purchased under pension plan, value per share					$ 60.45
Fair value of common shares held by pension plan		$ 11,900,000	$ 9,800,000
Fair value of common shares held by pension plan, per share		$ 102.38	$ 84.95
Fair value, pension plan common shares held, shares		115,800
Estimated net actuarial (loss) expected to be recognized in the next fiscal year		$ 1,200,000
Market value of pension plan assets		210,600,000	$ 177,100,000
Defined Contribution Plan, Cost		3,900,000	3,000,000.0	$ 1,300,000
Defined Benefit Plan, Plan Assets, Amount		210,623,000	177,077,000	195,735,000
Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 0
Level 1
Defined Benefit Plan Disclosure [Line Items]
Equity investments		180,000,000.0	147,100,000
Level 2
Defined Benefit Plan Disclosure [Line Items]
Equity investments		30,600,000	30,000,000.0
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity investments		0	0
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount		8,900,000
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated prior service costs expected to be recognized in net periodic benefit cost during next fiscal year		(16,000)
Supplemental Executive Retirement Plan (SERP)
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit cost		11,000,000.0	10,300,000
Benefit expense		$ 1,300,000	$ 1,000,000.0	$ 1,700,000