Income Taxes - Deferred tax liabilities and deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Property and equipment	$ 2,194
Benefit plans	787
Accrued compensation and related costs	11,779	$ 5,868
Other accrued expenses	2,780	3,861
Unrealized losses on investment securities and partnerships		6,272
Share-based compensation	9,215	10,300
Unused state tax credits	2,341	2,618
State net operating loss carryforwards	7,082	7,266
Operating lease liabilities	6,042
Other	1,061	1,171
Total gross deferred assets	43,281	37,356
Deferred tax liabilities:
Property and equipment		(3,700)
Benefit plans		(1,872)
Identifiable intangible assets	(9,301)	(9,206)
Unrealized gain on investments securities and partnerships	(3,469)
Prepaid expenses	(2,283)	(2,478)
Operating lease right-of-use assets	(5,630)
Other	(308)	(513)
Total gross deferred liabilities	(20,991)	(17,769)
Valuation allowance	(7,872)	(7,266)
Net deferred tax asset	14,418	12,321
Deferred tax assets, operating loss carryforwards, subject to expiration	7,100	7,300
Operating loss carryforward, valuation allowance	7,100	7,300
State tax credit carryforwards	2,300	$ 2,600
State tax credit carryforwards that will expire between 2024 and 2034 if not utilized	2,100
State tax credit carryforwards that will expire in 2026 if not utilized	200
State tax credit carryforwards, indefinite carryforward	100
State tax credit carryforwards, valuation allowance	$ 800