Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Defined Benefit Plan Net Periodic Benefit Cost [Line Items]
Service cost	$ 13,511	$ 12,920	$ 16,118
Interest cost	18,635	19,251	16,678
Expected return on plan assets	(32,833)	(32,222)	(27,928)
Amortization of net loss/ prior service cost	3,169	26	6,570
Net periodic benefit cost	2,482	(25)	11,438
Net (loss) gain recognized during the year	(3,169)	(26)	(6,570)
Net actuarial loss (gain)	39,876	44,599	(76,939)
Total recognized in other comprehensive income	36,707	44,573	(83,509)
Total recognized in net periodic benefit cost and other comprehensive income	$ 39,189	$ 44,548	$ (72,071)
Discount rate for benefit obligations	4.40%	4.11%	4.73%
Discount rate for net periodic benefit cost	4.11%	4.73%	3.82%
Expected long-term return on plan assets	7.50%	7.50%	7.50%
Rate of compensation increase			4.00%
Other Post-retirement Benefits [Member]
Defined Benefit Plan Net Periodic Benefit Cost [Line Items]
Service cost	$ 117	$ 126	$ 215
Interest cost	891	1,140	1,317
Amortization of net loss/ prior service cost	6	364	1,761
Net periodic benefit cost	1,014	1,630	3,293
Net (loss) gain recognized during the year	(6)	(364)	(1,761)
Net actuarial loss (gain)	(5,905)	(3,467)	(5,563)
Total recognized in other comprehensive income	(5,911)	(3,831)	(7,324)
Total recognized in net periodic benefit cost and other comprehensive income	$ (4,897)	$ (2,201)	$ (4,031)
Discount rate for benefit obligations	4.32%	4.02%	4.58%
Discount rate for net periodic benefit cost	4.02%	4.58%	3.69%