Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 22,013	$ 18,201	$ 61,135	$ 63,314
Change in net unrealized gains (losses) on investments:
Unrealized gains (losses) on investments arising during the period, net of deferred tax	(2,414)	1,018	43,362	(18,765)
Reclassification adjustment for net realized (gains) losses included in net income, net of deferred tax	(519)	(544)	1,449	(2,733)
Change in net unrealized gains (losses) on investments	(2,933)	474	44,811	(21,498)
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax	15	(15)	(64)	(32)
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income, net of deferred tax		188		316
Change in other-than-temporary impairments	15	173	(64)	284
Change in foreign currency translation gains (losses), net of deferred tax	(335)	1	(6,174)	12
Other comprehensive income (loss)	(3,253)	648	38,573	(21,202)
Comprehensive income (loss)	$ 18,760	$ 18,849	$ 99,708	$ 42,112