Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Change in Balance by Component of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	$ 1,165,641	$ 606,058	$ 997,452	$ 210,981
Other comprehensive income (loss) before reclassifications, net of tax	(610,696)	282,124	(443,708)	687,777
Reclassifications, net of tax	374	(208)	1,575	(10,784)
Other comprehensive income (loss)	(610,322)	281,916	(442,133)	676,993
Accumulated other comprehensive income (loss), Ending Balance	555,319	887,974	555,319	887,974
Available for Sale Assets [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	1,261,518	653,086	1,090,273	256,196
Other comprehensive income (loss) before reclassifications, net of tax	(609,544)	281,810	(437,135)	690,949
Reclassifications, net of tax	(2,001)	(1,881)	(3,165)	(14,130)
Other comprehensive income (loss)	(611,545)	279,929	(440,300)	676,819
Accumulated other comprehensive income (loss), Ending Balance	649,973	933,015	649,973	933,015
Deferred Acquisition Costs [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	(10,334)	(9,476)	(10,758)	(6,728)
Other comprehensive income (loss) before reclassifications, net of tax	1,919	(1,979)	2,343	(4,727)
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	1,919	(1,979)	2,343	(4,727)
Accumulated other comprehensive income (loss), Ending Balance	(8,415)	(11,455)	(8,415)	(11,455)
Foreign Exchange [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	11,424	24,128	17,386	24,866
Other comprehensive income (loss) before reclassifications, net of tax	(3,071)	1,996	(9,033)	1,258
Reclassifications, net of tax	0	0	0	0
Other comprehensive income (loss)	(3,071)	1,996	(9,033)	1,258
Accumulated other comprehensive income (loss), Ending Balance	8,353	26,124	8,353	26,124
Pension adjustments [Member]
Accumulated Other Comprehensive Income, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), Beginning Balance	(96,967)	(61,680)	(99,449)	(63,353)
Other comprehensive income (loss) before reclassifications, net of tax	0	297	117	297
Reclassifications, net of tax	2,375	1,673	4,740	3,346
Other comprehensive income (loss)	2,375	1,970	4,857	3,643
Accumulated other comprehensive income (loss), Ending Balance	$ (94,592)	$ (59,710)	$ (94,592)	$ (59,710)