Consolidated Statements Of Operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Net premiums earned	$ 868,233	$ 858,135	$ 833,959	$ 808,084	$ 806,796	$ 801,205	$ 797,666	$ 789,770	$ 3,368,411	$ 3,195,437	$ 3,131,773
Net investment income									135,838	124,930	121,871
Net realized investment (losses) gains									(133,520)	83,650	(34,255)
Other									9,275	11,945	8,294
Total revenues									3,380,004	3,415,962	3,227,683
Expenses:
Losses and loss adjustment expenses									2,576,789	2,444,884	2,355,138
Policy acquisition costs									572,164	555,350	562,545
Other operating expenses									244,630	233,475	235,314
Interest									17,036	15,168	3,962
Total expenses									3,410,619	3,248,877	3,156,959
(Loss) income before income taxes	(114,448)	70,286	73,246	(59,699)	9,487	58,247	68,752	30,599	(30,615)	167,085	70,724
Income tax (benefit) expense									(24,887)	22,208	(2,320)
Net (loss) income	$ (81,879)	$ 58,578	$ 60,180	$ (42,607)	$ 19,779	$ 46,485	$ 51,633	$ 26,980	$ (5,728)	$ 144,877	$ 73,044
Net (loss) income per share:
Basic (in dollars per share)	$ (1.48)	$ 1.06	$ 1.09	$ (0.77)	$ 0.36	$ 0.84	$ 0.93	$ 0.49	$ (0.10)	$ 2.62	$ 1.32
Diluted (in dollars per share)	$ (1.48)	$ 1.06	$ 1.09	$ (0.77)	$ 0.36	$ 0.84	$ 0.93	$ 0.49	$ (0.10)	$ 2.62	$ 1.32