Derivative Financial Instruments and Fair Value Measurements - SERP Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
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	$ 4	$ 6
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	1,819	1,693
Level 1 | 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	0	0
Level 1 | 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	0	0
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	4	6
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	1,819	1,693
Level 3 | 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	0	0
Level 3 | 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	$ 0	$ 0