Accumulated Other Comprehensive Loss - Related Tax Effects Allocated to Each Component of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 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	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Before Tax Amount
Total other comprehensive income													$ 2,426	$ (6,477)
Tax Expense
Total other comprehensive income													(905)	241
After Tax Amount
Net unrealized gain	$ 3,743	$ (2,095)	$ 1,739	$ (649)	$ 935	$ (1,060)	$ (594)	$ (338)	$ 1,090	$ (932)	$ (1,005)	$ (1,992)	2,738	(1,057)	$ 469
Cumulative translation adjustment	1,866	(3,388)	233	104	(312)	(1,529)	(5,304)	1,470	337	(3,834)	(3,051)	(5,363)	(1,185)	(5,675)	7,141
Derivative instruments	161	(515)	(17)	339	496	0	0	0	322	0	(193)	0	(32)	496	0
Other comprehensive income (loss)	$ 5,770	$ (5,998)	$ 1,955	$ (206)	$ 1,119	$ (2,589)	$ (5,898)	$ 1,132	$ 1,749	$ (4,766)	$ (4,249)	$ (7,355)	1,521	(6,236)	$ 7,610
Retirement benefits adjustment:
Before Tax Amount
Net actuarial gain and prior service credit													3,320	(1,531)
Reclassification of actuarial loss and prior service cost to net income													323	233
Total recognized in other comprehensive income (loss)													3,643	(1,298)
Tax Expense
Net actuarial gain and prior service credit													(905)	241
Reclassification of actuarial loss and prior service cost to net income													0	0
Net unrealized gain													(905)	241
After Tax Amount
Net actuarial gain and prior service credit													2,415	(1,290)
Reclassification of actuarial loss and prior service cost to net income													323	233
Net unrealized gain													2,738	(1,057)
Cumulative translation adjustment
Before Tax Amount
Cumulative translation adjustment													(1,185)	(5,675)
Tax Expense
Cumulative translation adjustment													0	0
After Tax Amount
Cumulative translation adjustment													(1,185)	(5,675)
Derivative Instruments
Before Tax Amount
Derivative instruments													(32)	496
Tax Expense
Derivative instruments													0	0
After Tax Amount
Derivative instruments													$ (32)	$ 496