Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Comprehensive Income (Loss) [Abstract]
Net income (loss)	$ (24,567)	$ (12,325)	$ 2,487	$ 330	$ 16,476	$ 7,434	$ (12,343)	$ 6,756	$ (34,075)	$ 18,323	$ 28,945
Unrealized net gains (losses) on fixed income securities:
Unrealized net gains (losses) arising during the period									(9,680)	17,340	8,618
Less: reclassification adjustment for net gains (losses) included in net income (loss)									(2,812)	4,691	13,491
Change in unrealized gains (losses) on investments									(6,868)	12,649	(4,873)
Foreign currency translation adjustments									(830)	522	235
Other comprehensive income (loss)									(7,698)	13,171	(4,638)
Comprehensive income (loss)									$ (41,773)	$ 31,494	$ 24,307