Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 22,932	$ 25,929
Change in net unrealized gains (losses) on investments:
Unrealized gains (losses) on investments arising during the period, net of deferred tax of $(11,737) and $(1,723) in 2016 and 2015, respectively	21,798	3,201
Reclassification adjustment for net realized (gains) losses included in net income net of deferred tax of $(758) and $698 in 2016 and 2015, respectively	1,408	(1,297)
Change in net unrealized gains (losses) on investments	23,206	1,904
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $38 and $(8) in 2016 and 2015, respectively	(71)	15
Change in other-than-temporary impairments	(71)	15
Change in foreign currency translation gains (losses), net of deferred tax of $183 and $429 in 2016 and 2015, respectively	(346)	(796)
Other comprehensive income (loss)	22,789	1,123
Comprehensive income (loss)	$ 45,721	$ 27,052