Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Components of Other Comprehensive Income (Loss) [Abstract]
Net unrealized holding (losses) gains arising during the period		$ 78,383	$ 19,721
Income tax expense		(27,556)	(6,876)
Valuation allowance	[1]	0	6,718
Net of taxes		50,827	19,563
Net changes in benefit plan assets and obligations		(474)	(700)
Income tax benefit		166	245
Valuation allowance	[1]	0	(245)
Net of taxes		(308)	(700)
Net changes in unrealized foreign currency translation adjustment		(1,496)	(3,102)
Income tax benefit		521	1,088
Net of taxes		(975)	(2,014)
Total other comprehensive income (loss)		76,413	15,919
Total income tax (expense) benefit, net of valuation allowance		(26,869)	930
Other comprehensive income (loss), net of tax		49,544	16,849
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications		103,688	136,461
Income tax expense		(34,497)	(47,883)
Valuation allowance		0	(44,498)
Total income tax expense, net of valuation allowance		(34,497)	(3,385)
Net income		69,191	133,076
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period, net of tax		(60,880)
Other comprehensive loss before reclassifications		50,372
Less: Amounts reclassified from AOCL		828
Balance at end of period, net of tax		(11,336)
Net unrealized gains and losses on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period, net of tax		(17,148)
Other comprehensive loss before reclassifications		51,347
Less: Amounts reclassified from AOCL		520
Balance at end of period, net of tax		33,679
Net benefit plan assets and obligations recognized in shareholders' equity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period, net of tax		(44,652)
Other comprehensive loss before reclassifications		0
Less: Amounts reclassified from AOCL		308
Balance at end of period, net of tax		(44,960)
Net unrealized foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period, net of tax		920
Other comprehensive loss before reclassifications		(975)
Less: Amounts reclassified from AOCL		0
Balance at end of period, net of tax		(55)
Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications		1,086	11,934
Total income tax expense, net of valuation allowance		(258)	(5)
Net income		828	11,929
Reclassification from Accumulated Other Comprehensive Income | Net unrealized gains and losses on available-for-sale securities
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications	[2]	612	11,234
Income tax expense		(92)	(3,931)
Valuation allowance	[3]	0	3,926
Net income		520	11,229
Reclassification from Accumulated Other Comprehensive Income | Net benefit plan assets and obligations recognized in shareholders' equity
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Total reclassifications	[4]	474	700
Income tax expense		(166)	(245)
Valuation allowance	[3]	0	245
Net income		$ 308	$ 700

[1] See Note 11 – “Income Taxes” for a discussion of the valuation allowance recorded against deferred tax assets.

[2] Increases (decreases) Net realized investment gains on the consolidated statements of operations.

[3] See Note 11 – “Income Taxes” for a discussion of the valuation allowance recorded against deferred tax assets.

[4] Decreases (increases) Other underwriting and operating expenses, net on the consolidated statements of operations.