CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 84,268	$ 112,120	$ 159,682	$ 227,468
Other comprehensive income (loss):
Change in net unrealized gains (losses) on investments, net of income tax: (three months: 2017 - $155,316; 2016 - $314,161; six months: 2017 - $241,278; 2016 - $550,511)	288,445	583,441	448,086	1,022,377
Reclassification adjustment for investment amounts included in net income, net of income tax: (three months: 2017 - $1,355; 2016 - $(5,588); six months: 2017 - $777; 2016 - $(6,616))	2,517	(10,377)	1,445	(12,287)
Change in net unrealized gains (losses) relating to other-than-temporary impaired investments for which a portion has been recognized in earnings, net of income tax: (three months: 2017 - $1,390; 2016 - $(1,543); six months: 2017 - $3,385; 2016 - $(1,384))	2,583	(2,866)	6,286	(2,572)
Change in accumulated (loss) gain - derivatives, net of income tax: (three months: 2017 - $(64); 2016 - $0; six months: 2017 - $(426); 2016 - $0)	(120)	0	(792)	0
Reclassification adjustment for derivative amounts included in net income, net of income tax: (three months: 2017 - $53; 2016 - $0; six months: 2017 - $125; 2016 - $0)	100	0	233	0
Total other comprehensive income	293,525	570,198	455,258	1,007,518
Total comprehensive income	$ 377,793	$ 682,318	$ 614,940	$ 1,234,986