Equity - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 378,156
Income tax (expense) benefit	630	$ (1,052)
Other comprehensive income (loss), net of tax	(1,332)	(4,424)	$ 2,779
Ending balance	469,577	378,156
AOCI Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(26,692)	(22,268)	(25,047)
Unrealized gains (losses) arising during period	(2,231)	(3,432)	2,599
Amounts reclassified from accumulated other comprehensive loss	269	60	180
Income tax (expense) benefit	630	(1,052)
Other comprehensive income (loss), net of tax	(1,332)	(4,424)	2,779
Ending balance	(28,024)	(26,692)	(22,268)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(20,149)	(22,268)	(25,047)
Unrealized gains (losses) arising during period	(2,231)	3,111	2,599
Amounts reclassified from accumulated other comprehensive loss	(64)	60	180
Income tax (expense) benefit	630	(1,052)
Other comprehensive income (loss), net of tax	(1,665)	2,119	2,779
Ending balance	(21,814)	(20,149)	$ (22,268)
Accumulated Other-than-Temporary Impairment Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(6,543)
Unrealized gains (losses) arising during period		(6,543)
Amounts reclassified from accumulated other comprehensive loss	333
Other comprehensive income (loss), net of tax	333	(6,543)
Ending balance	$ (6,210)	$ (6,543)