Supplemental Executive Retirement Plans - Plan Details and Change in Benefit Obligation (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) payment	Sep. 30, 2018 USD ($)	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	$ 17,535	$ 19,388	$ 18,927	$ 20,793
Service cost	84	92	251	275
Interest cost	164	150	494	450
Payments	(12)	(13)	(1,901)	(1,901)
Benefit obligation at the end of the period	17,771	$ 19,617	17,771	$ 19,617
Amounts Recognized in the Condensed Consolidated Balance Sheets:
Accrued expenses and other current liabilities	1,913		1,913		$ 1,913
Other liabilities	15,858		15,858		17,014
Total accrued liabilities	$ 17,771		$ 17,771		$ 18,927