Derivative Financial Instruments - Changes in Fair Value of Derivative Contracts (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:
Other comprehensive income (loss)	$ 2,124	$ 881	$ (418)
Derivative contracts
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax:
Beginning balance	5,852	6,937
Loss recognized in other comprehensive loss	(1,729)	669
Amounts reclassified from other comprehensive loss to earnings	(369)	(1,563)
Other comprehensive income (loss)	(2,098)	(894)
Ending balance	3,548	5,852	$ 6,937
Interest rate swap agreements
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax:
Gain recognized in earnings	$ (206)	$ (191)

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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