Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Gross written premiums		$ 450,305	$ 413,877
Revenues:
Net written premiums		337,163	319,820
Change in unearned premiums		(51,032)	(55,462)
Net earned premiums		286,131	264,358
Net investment income		21,448	19,594
Total other-than-temporary impairment losses		(1,077)	(109)
Portion of loss recognized in other comprehensive income (before tax)		(16)	109
Net other-than-temporary impairment losses recognized in earnings		(1,093)	0
Net realized gains		1,049	1,597
Other income		1,068	2,549
Total revenues		308,603	288,098
Expenses:
Net losses and loss adjustment expenses		169,600	152,956
Commission expenses		47,844	37,554
Other operating expenses		58,538	60,809
Interest expense		3,861	3,858
Total expenses		279,843	255,177
Income before income taxes		28,760	32,921
Income tax expense		7,650	9,989
Net income		$ 21,110	$ 22,932
Net income per common share:
Basic	[1]	$ 0.72	$ 0.79
Diluted	[1]	$ 0.70	$ 0.77
Average common shares outstanding:
Basic	[1]	29,283	28,984
Diluted	[1]	30,000	29,783
Cash dividends declared per common share		$ 0.045	$ 0

[1] We completed a two-for-one stock split on January 20, 2017. All share and per share data prior to January 20, 2017 has been retroactively restated on a post-split basis.