Accumulated Other Comprehensive Income - Reclassification Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains on investments										$ 1,165	$ 658	$ 305
Tax effect										(21,250)	(10,493)	(109)
Income from continuing operations		$ (4,136)	$ 34,013	$ 19,873	$ (6,797)	$ (796)	$ 7,393	$ 22,311	$ (1,908)	43,479	27,442	$ 41,178
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										(97)	(112)
Tax effect										37	42
Income from continuing operations										(60)	(70)
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]									1,440	1,180
Amortization of prior service credit	[1]									(575)	(552)
Tax effect										(328)	(159)
Income from continuing operations										$ 537	$ 469

[1] Amount included in pension expense. Refer to Note 17 – Pension and Postretirement Benefits