CONSOLIDATED CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 81,495	$ 84,268	$ 155,607	$ 159,682
Other comprehensive income (loss):
Change in net unrealized gains (losses) on investments, net of income tax: (three months: 2018 - $(113,653); 2017 - $155,316; six months: 2018 - $(267,032); 2017 - $241,278)	(427,550)	288,445	(1,005,262)	448,086
Reclassification adjustment for investment amounts included in net income, net of income tax: (three months: 2018 - $(1,162); 2017 - $1,355; six months: 2018 - $(981); 2017 - $777)	(4,372)	2,517	(3,691)	1,445
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: 2018 - $3; 2017 - $1,390; six months: 2018 - $6; 2017 - $3,385)	11	2,583	22	6,286
Change in accumulated (loss) gain - derivatives, net of income tax: (three months: 2018 - $623; 2017 - $(64); six months: 2018 - $752; 2017 - $(426))	2,344	(120)	2,831	(792)
Reclassification adjustment for derivative amounts included in net income, net of income tax: (three months: 2018 - $43; 2017 - $53; six months: 2018 - $67; 2017 - $125)	162	100	251	233
Total other comprehensive income (loss)	(429,405)	293,525	(1,005,849)	455,258
Total comprehensive income (loss)	$ (347,910)	$ 377,793	$ (850,242)	$ 614,940