Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating Activities
Net income	$ 138,716	$ 100,209
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on the sale of investments, net	(1,199)	(1,054)
Depreciation and amortization	1,970	2,040
Stock-based compensation expense	9,288	7,949
Amortization of premium on investment securities	5,833	5,218
Deferred income tax provision	32,948	28,264
Change in:
Accrued investment income	(1,288)	(712)
Accounts receivable	(4,134)	(2,478)
Deferred policy acquisition costs	(637)	(710)
Prepaid federal income tax	(34,085)	(30,360)
Other assets	(1,877)	(375)
Reserve for losses and LAE	1,656	4,714
Unearned premium reserve	9,146	13,865
Other accrued liabilities	(11,934)	(3,480)
Net cash provided by operating activities	144,403	123,090
Investing Activities
Net change in short-term investments	1,364	(43,239)
Purchase of investments available for sale	(396,919)	(268,024)
Proceeds from maturity of investments available for sale	36,318	9,043
Proceeds from sales of investments available for sale	151,583	178,719
Purchase of property and equipment	(1,806)	(2,049)
Net cash used in investing activities	(209,460)	(125,550)
Financing Activities
Credit facility borrowings	200,000	0
Credit facility repayments	(125,000)	0
Treasury stock acquired	(7,239)	(3,876)
Payment of issuance costs for credit facility	(2,565)	(2,098)
Net cash provided by (used in) financing activities	65,196	(5,974)
Net increase (decrease) in cash	139	(8,434)
Cash at beginning of year	27,531	24,606
Cash at end of period	27,670	16,172
Supplemental Disclosure of Cash Flow Information
Income tax payments	(16,700)	(10,800)
Interest payments	$ (1,772)	$ 0