Supplemental Executive Retirement Plans - Plan Details and Change in Benefit Obligation (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) payment	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Supplemental Executive Retirement Plans
Number of annual payments | payment			15
Change in Benefit Obligation
Benefit obligation at the beginning of the period	$ 17,299	$ 19,158	$ 18,927	$ 20,793
Service cost	84	92	168	184
Interest cost	164	150	329	300
Payments	(12)	(12)	(1,889)	(1,889)
Benefit obligation at the end of the period	17,535	$ 19,388	17,535	$ 19,388
Amounts Recognized in the Consolidated Balance Sheets:
Accrued expenses and other current liabilities	1,913		1,913		$ 1,913
Other liabilities	15,622		15,622		17,014
Total accrued liabilities	$ 17,535		$ 17,535		$ 18,927