Derivative Financial Instruments and Fair Value Measurements - SERP Assets Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Money market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
SERP assets measured at fair value on a recurring basis	$ 6	$ 22
Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
SERP assets measured at fair value on a recurring basis	1,693	1,785
Level 2 | Money market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
SERP assets measured at fair value on a recurring basis	6	22
Level 2 | Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
SERP assets measured at fair value on a recurring basis	$ 1,693	$ 1,785