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Share-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized under stock incentive plan (in shares)	30,600,000
Number of shares available for grant under stock incentive plan (in shares)	2,400,000
Share-based compensation expense	$ 26,669	$ 25,057	$ 23,893
Tax benefit from share-based compensation	6,400	$ 6,000	$ 5,600
Nonvested awards, total compensation cost not yet recognized	$ 76,000
Nonvested awards, total compensation cost not yet recognized, period for recognition	6 years
Restricted stock granted in period (in shares)	1,134,581	928,324	899,269
Restricted stock granted in period, weighted average grant date fair value (usd per share)	$ 25.98	$ 30.10	$ 28.30
Restricted stock, vested in period, total fair value	$ 23,200	$ 28,400	$ 24,000
Class B Common Stock Bonus
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period	3 years
Restricted stock granted in period (in shares)	649,581
Class B Common Stock Bonus \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period	3 years
Class B Common Stock Bonus \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period	10 years
Class B Common Stock Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service period	10 years
Restricted stock granted in period (in shares)	485,000
Subsidiary Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested awards, total compensation cost not yet recognized	$ 25,000
Nonvested awards, total compensation cost not yet recognized, period for recognition	3 years
Compensation and related expense	$ 8,800	$ 7,900	$ 4,200
Subsidiary Stock Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Subsidiary Stock Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years