Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Analysis of Change in Balance by Component of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	$ 555,319	$ 887,974	$ 997,452	$ 210,981
Other comprehensive income (loss) before reclassifications, net of tax	(53,238)	(6,105)	(496,946)	681,672
Reclassifications, net of tax	(2,252)	958	(677)	(9,826)
Other comprehensive income (loss)	(55,490)	(5,147)	(497,623)	671,846
Accumulated other comprehensive income (loss), ending balance	499,829	882,827	499,829	882,827
Available for Sale Assets [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	649,973	933,015	1,090,273	256,196
Other comprehensive income (loss) before reclassifications, net of tax	(48,306)	(1,991)	(485,441)	688,958
Reclassifications, net of tax	(4,621)	(711)	(7,786)	(14,841)
Other comprehensive income (loss)	(52,927)	(2,702)	(493,227)	674,117
Accumulated other comprehensive income (loss), ending balance	597,046	930,313	597,046	930,313
Deferred Acquisition Costs [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	(8,415)	(11,455)	(10,758)	(6,728)
Other comprehensive income (loss) before reclassifications, net of tax	934	450	3,277	(4,277)
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	934	450	3,277	(4,277)
Accumulated other comprehensive income (loss), ending balance	(7,481)	(11,005)	(7,481)	(11,005)
Foreign Exchange [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	8,353	26,124	17,386	24,866
Other comprehensive income (loss) before reclassifications, net of tax	(5,867)	(4,566)	(14,900)	(3,308)
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	(5,867)	(4,566)	(14,900)	(3,308)
Accumulated other comprehensive income (loss), ending balance	2,486	21,558	2,486	21,558
Pension Adjustments [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	(94,592)	(59,710)	(99,449)	(63,353)
Other comprehensive income (loss) before reclassifications, net of tax	1	2	118	299
Reclassifications, net of tax	2,369	1,669	7,109	5,015
Other comprehensive income (loss)	2,370	1,671	7,227	5,314
Accumulated other comprehensive income (loss), ending balance	$ (92,222)	$ (58,039)	$ (92,222)	$ (58,039)