Nature of Business - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales									$ (310,894)	$ (325,712)	$ (363,265)
Defined benefit plan adjustments – actuarial losses									5,091	2,139
Income (Loss) Before Income Taxes									(24,777)	(33,371)	44,687
Tax benefit (expense)									(28,205)	14,029	(20,847)
Total reclassifications for the period, net of tax	$ (11,624)	$ (46,123)	$ 3,995	$ 770	$ (8,447)	$ 7,589	$ (7,670)	$ (10,814)	(52,982)	(19,342)	23,840
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan adjustments – actuarial losses									(771)	(196)	(406)
Income (Loss) Before Income Taxes									(374)	608	3,381
Tax benefit (expense)									136	(148)	(1,423)
Total reclassifications for the period, net of tax									(238)	460	1,958
Unrealized Gains (Losses) on Available-for-Sale Securities [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gain (loss)									$ 397	$ 804	4,864
Impairment Expense [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gain (loss)											(180)
Net Losses on Derivatives Designated as Hedging Instruments [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales											$ (897)