Retirement plans - Narrative (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
401(k) employee maximum matching contribution (up to)		50.00%
401(k) employer matching contribution		100.00%
Contributions per employee subject to employer match		4.00%
Compensation expense related to 401(k) contributions		$ 17,100,000	$ 16,500,000	$ 14,600,000
Expenses incurred for multi-employer withdrawal liabilities		0	0	$ 0
Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarial (gain)/loss		$ 18,246,000	$ (48,491,000)
Discount rate (as a percent)	3.29%	2.89%	2.54%	3.29%
Actuarial gain (losses) from change in discount rate		$ 22,100,000	$ (49,300,000)
Accumulated benefit obligation		605,817,000	646,644,000
Discretionary contributions by employer	$ 12,000,000
Contributions made to SERP		6,337,000	$ 5,133,000
Contributions expected to be made during next fiscal year		$ 5,900,000
Target allocation (as a percent)		100.00%
Actual rate of return on plan assets (as a percent)		4.50%	23.50%	23.60%
Retirement Plans | Corporate stock
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation (as a percent)		14.00%
Retirement Plans | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation (as a percent)		86.00%
SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions made to SERP		$ 6,300,000
AFTRA Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Funded percentage		78.00%
Contribution by employer		$ 2,900,000	$ 2,400,000	$ 2,400,000