Retirement Benefit Plans (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 01, 2015
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 227,200	$ 218,000
Net actuarial loss	$ 6,500
Assumed healthcare cost trend (as a percent)	8.25%
Healthcare-cost trend rate in 2024 (as a percent)	4.75%
Employer matching contribution, percent of match	100.00%
Employer matching contribution, percent of employees' gross pay	2.00%
Employer matching contribution, additional percent of match	50.00%
Employer additional matching contribution, percent of employees' gross pay	6.00%
Compensation expense	$ 11,100	10,900	$ 10,600
Multiemployer Plans, Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status of plan				$ (1,100)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 20,000	$ 0
Expected long-term return on assets (as a percent)	7.00%	7.00%	7.25%
Funded status of plan	$ (18,586)	$ (42,276)
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	124	241
Funded status of plan	(11,806)	(10,518)
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 185	$ 225
Assumed healthcare cost trend (as a percent)	8.25%	8.00%
Increase in net periodic postretirement benefit cost if trend increased by 1%	$ 6
Increase in accumulated benefit obligation if trend increased by 1%	205
Decrease in net periodic postretirement benefit cost if trend rate decreased by 1%	6
Decrease in accumulated benefit obligation if trend rate decreased 1%	185
Funded status of plan	$ (3,852)	$ (3,853)
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of employees' gross pay	3.00%