Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 82,726	$ 81,057	$ 95,329
Change in net unrealized gains (losses) on investments:
Unrealized gains (losses) on investments arising during the period, net of deferred tax of $3,730, $2,624, and $(14,925) in 2016, 2015 and 2014 respectively	(6,927)	(5,331)	28,252
Reclassification adjustment for net realized (gains) losses included in net income net of deferred tax of $(846), $9,185, and $2,776 in 2016, 2015 and 2014 respectively	1,572	(17,058)	(5,156)
Change in net unrealized gains (losses on investments)	(5,355)	(22,389)	23,096
Change in other-than-temporary impairments:
Non credit other-than-temporary impairments arising during the period, net of deferred tax of $27, $60, and $(48) in 2016, 2015 and 2014 respectively	(50)	(112)	89
Reclassification adjustment for other-than-temporary impairment credit losses recognized in net income net of deferred tax of $0, $(90), and $0 in 2016, 2015 and 2014 respectively		168
Change in other-than-temporary impairments	(50)	56	89
Change in foreign currency translation gains (losses), net of deferred tax of $5,017, $351, and $2,800 in 2016, 2015 and 2014 respectively	(9,324)	(622)	(4,986)
Other comprehensive income (loss)	(14,729)	(22,955)	18,199
Comprehensive income (loss)	$ 67,997	$ 58,102	$ 113,528