Stock Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Contribution expense	$ 6,874	$ 6,921	$ 6,644
Retirement Savings Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer match of employee contributions to Retirement Savings Plan	50.00%
Maximum salary percentage of employer match	6.00%
Contribution expense	$ 4,149	$ 4,333	$ 4,088
Shares held by Retirement Savings Plan	812,362