Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 18,201	$ 31,225	$ 63,314	$ 76,054
Change in net unrealized gains (losses) on investments:
Unrealized gains (losses) on investments arising during the period, net of deferred tax of $(549) and $8,231 for the three months ended September 30, 2015 and 2014 and $9,858 and $4,951 for the nine months ended September 30, 2015 and 2014, respectively	1,018	(15,405)	(18,765)	9,576
Reclassification adjustment for net realized (gains) losses included in net income net of deferred tax of $293 and $2,581 for the three months ended September 30, 2015 and 2014 and $1,472 and $3,088 for the nine months ended September 30, 2015 and 2014, respectively	(544)	4,794	(2,733)	5,736
Change in net unrealized gains (losses) on investments	474	(10,611)	(21,498)	15,312
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $8 and $14 for the three months ended September 30, 2015 and 2014 and $17 and $55 for the nine months ended September 30, 2015 and 2014, respectively	(15)	(27)	(32)	103
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income net of deferred tax of $(101) and $0 for the three months ended September 30, 2015 and 2014 and $(170) and $0 for the nine months ended September 30, 2015 and 2014, respectively	188		316
Change in other-than-temporary impairments	173	(27)	284	103
Change in foreign currency translation gains (losses), net of deferred tax of $(1) and $0 for the three months ended September 30, 2015 and 2014 and $6 and $2,800 for the nine months ended September 30, 2015 and 2014, respectively	1	41	12	(4,956)
Other comprehensive income (loss)	648	(10,597)	(21,202)	10,459
Comprehensive income (loss)	$ 18,849	$ 20,628	$ 42,112	$ 86,513