Stockholders' Equity - Reclassification out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains on investments		$ 38	$ 443	$ 94	$ 506
Tax effect		(9,226)	(10,372)	(5,774)	(7,105)
Income from continuing operations		$ 19,808	$ 22,202	12,849	20,230
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				(25)	(54)
Tax effect				9	20
Income from continuing operations				(16)	(34)
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]			388	345
Amortization of prior service credit	[1]			(251)	(275)
Tax effect				(52)	(101)
Income from continuing operations				$ 85	$ (31)

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