Schedule II-Condensed Financial Information of Registrant (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments available for sale, at fair value
Fixed maturities	$ 1,482,754	$ 1,190,638
Short-term investments	132,348	85,996
Total investments	1,615,102	1,276,634
Cash	27,531	24,606
Other assets	6,454	3,492
Total assets	1,882,998	1,469,099
Liabilities
Revolving credit facility borrowings	100,000	0
Other accrued liabilities	33,881	28,093
Total liabilities	539,225	349,858
Commitments and contingencies (see Note 8)
Stockholders' Equity
Common shares	1,397	1,390
Additional paid-in capital	918,296	904,221
Accumulated other comprehensive loss	(12,255)	(99)
Retained earnings	436,335	213,729
Total stockholders' equity	1,343,773	1,119,241	$ 955,738	$ 722,141
Total liabilities and stockholders' equity	1,882,998	1,469,099
Parent Company
Investments available for sale, at fair value
Fixed maturities	10,004	36,549
Short-term investments	32,036	25,511
Total investments	42,040	62,060
Cash	4,521	8,541
Due from affiliates	1,750	1,021
Investment in consolidated subsidiaries	1,393,720	1,047,114
Other assets	2,452	866
Total assets	1,444,483	1,119,602
Liabilities
Revolving credit facility borrowings	100,000	0
Other accrued liabilities	710	361
Total liabilities	100,710	361
Commitments and contingencies (see Note 8)
Stockholders' Equity
Common shares	1,397	1,390
Additional paid-in capital	918,296	904,221
Accumulated other comprehensive loss	(12,255)	(99)
Retained earnings	436,335	213,729
Total stockholders' equity	1,343,773	1,119,241
Total liabilities and stockholders' equity	$ 1,444,483	$ 1,119,602