Stockholders' Equity - Reclassification out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains on investments		$ 44	$ 65	$ 138	$ 571
Tax effect		(17,878)	(3,746)	(23,652)	(10,851)
Income from continuing operations		$ 35,005	$ 8,081	47,854	28,311
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains on Investments
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains on investments				(67)	(79)
Tax effect				25	30
Income from continuing operations				(42)	(49)
Reclassification out of Accumulated Other Comprehensive Income | Unrecognized Net Actuarial Loss and Prior Service Credit, Net
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Recognized net actuarial (gain) loss	[1]			538	569
Amortization of prior service credit	[1]			(377)	(414)
Tax effect				(61)	(133)
Income from continuing operations				$ 100	$ 22

[1] Amount included in pension expense. Refer to Note 16 - Pension and Postretirement Benefits.