Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net unrealized holding gains (losses) on investments arising during the period, tax provision (benefit)	$ (370)	$ 5,907
Less: reclassification adjustment for net (gains) losses included in net income (loss), tax provision (benefit)	(5)	(11)
Net change in unrealized holding gains (losses) on investments, tax provision (benefit)	(365)	5,918
Net unrealized foreign exchange gains (losses) arising during the period, tax provision (benefit)	1,926	1,511
Less: reclassification adjustment for foreign exchange (gains) losses included in net income (loss), tax provision (benefit)	0	1,097
Net change in unrealized foreign exchange gains (losses), tax provision (benefit)	1,926	414
Net change in unrealized instrument specific credit risk gains (losses), tax provision (benefit)	(4,634)	(6,345)
Net change in unrealized cash flow hedges gains (losses), tax provision (benefit)	1,234	0
Less: reclassification adjustment for pension (gains) losses included in net income (loss), tax provision (benefit)	$ (151)	$ (1,435)