Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income	$ 139,779	$ 142,797	$ 208,949	$ 114,486	$ 6,816		$ 65,142	$ (27,342)	$ 76,472	$ 606,011	$ 121,088	$ 308,253
Unrealized gains (losses) on investments:
Unrealized holding gains (losses) arising during the period										(97,356)	31,903	8,782
Less: Reclassification adjustment for net gains (losses) included in net income										(10,270)	(2,642)	2,251
Net unrealized gains (losses) on investments, net of tax										(87,086)	34,545	6,531
Unrealized foreign currency translation adjustments										5	150	(474)
Less: Reclassification adjustment for liquidation of foreign subsidiary and other adjustments included in net income										1	(721)	0
Net foreign currency translation adjustments										4	871	(474)
Net actuarial gains										129	64	25
OCI, net of tax										(86,953)	35,480	6,082
Comprehensive income										$ 519,058	$ 156,568	$ 314,335

[1] The fourth quarter of 2017 reflects an incremental tax provision related to the remeasurement of our net deferred tax assets as a result of the enactment of the TCJA.