Stock Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Contribution expense	$ 5,301	$ 6,874	$ 6,921
Retirement Savings Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual retirement contribution percent	4.00%
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	$ 3,679	$ 4,149	$ 4,333
Shares held by Retirement Savings Plan	732,811