Stock Compensation Plans and Other Employee Benefit Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) hour shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 shares	May 31, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants (in shares) | shares	2,100,000
Stock-based compensation expense	$ (4,900,000)	$ 11,300,000	$ 13,500,000
Tax benefit (expense) from stock-based compensation arrangements	(914,000)	2,600,000	3,100,000
Aggregate intrinsic value of options exercised	4,100,000	4,700,000	13,300,000
Actual tax benefit realized from option exercises	1,100,000	1,300,000	3,500,000
Cash received from option exercises	9,700,000	5,700,000	11,700,000
Excess (deficit) tax benefit over estimate	(848,000)	870,000	994,000
Unrecognized compensation cost	$ 5,700,000
Unrecognized compensation cost, period for recognition	2 years
Fair value of shares vested	$ 14,700,000	9,800,000	8,000,000.0
Number of hours of service required for eligibility | hour	501
Expense for employer contribution to plan	$ 13,800,000	12,300,000	10,400,000
Pension expense (income)	$ 0	487,000	(38,000)
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout percentage	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout percentage	150.00%
Cash Incentive and Retention Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense related to plan	$ 0	0	0
Cash awards paid	0	$ 0	$ 0
Cash awards outstanding	$ 0
Directors Deferred Fee and Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares authorized (in shares) | shares	200,000
Issued to directors (in shares) | shares	19,928	18,577	18,856
Obligation to issue (in shares) | shares	331,482
Available for future issuance under DDFS Plan (in shares) | shares	186,129
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized (in shares) | shares					5,485,000
2015 and 2007 Plans | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
2015 and 2007 Plans | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
Option term	7 years
Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that could be issued based on the grants made to date (in shares) | shares	234,794	144,328	143,263	127,787
Restricted Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Restricted Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
LTIP Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that could be issued based on the grants made to date (in shares) | shares	482,608	465,515	396,855	359,196
Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares that could be issued based on the grants made to date (in shares) | shares	707,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of shares (as a percent)	95.00%
Employee stock purchase plan issuance (in shares) | shares	75,763	43,386	33,977
Compensation expense employee stock purchase plan	$ 0	$ 0	$ 0
Increase in shares authorized (in shares) | shares			200,000
Common stock obligation to issue (in shares) | shares	14,056
Available for future grants under ESPP (in shares) | shares	96,914