Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 21,110	$ 22,932
Change in net unrealized gains on investments:
Unrealized gains on investments arising during the period, net of deferred tax of $(7,771) and $(11,737) in 2017 and 2016, respectively	14,434	21,798
Reclassification adjustment for net realized losses included in net income net of deferred tax of $(114) and $(758) in 2017 and 2016, respectively	211	1,408
Change in net unrealized gains on investments	14,645	23,206
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $(6) and $38 in 2017 and 2016, respectively	10	(71)
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income net of deferred tax of $(222) and $0 in 2017 and 2016, respectively	412	0
Change in other-than-temporary impairments	422	(71)
Change in foreign currency translation losses, net of deferred tax of $143 and $183 in 2017 and 2016, respectively	(266)	(346)
Other comprehensive income	14,801	22,789
Comprehensive income	$ 35,911	$ 45,721