Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income Reclassifications (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized securities gains	$ 23,028	$ 29,542	$ 62,957
Reclassifications for the period, net of tax	(5,615)	(1,530)
Net unrealized gains on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications for the period, tax	124	2
Net unrealized foreign exchange losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications for the period, tax	(1,086)	0
Net minimum pension liability
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications for the period, net of tax	(1,748)	(1,534)
Reclassifications for the period, tax	(811)	(700)
Other pension
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications for the period, tax	1,231	0
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized gains on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized securities gains	212	4
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized foreign exchange losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income and other expenses	$ (5,310)	$ 0