Schedule I - Condensed Financial Information of the Parent (Condensed Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Cash and cash equivalents	$ 88,450	$ 122,892
Accounts receivable from affiliates	4,764	6,411
Other non-current assets	40,984	32,133
Total assets	476,179	444,773
LIABILITIES AND EQUITY
Current liabilities	52,257	61,966
Current portion of deferred compensation	0	13,465
Other long-term liabilities	12,060	6,188
Stockholders’ equity	300,624	289,392	$ 250,704
Total liabilities and equity	476,179	444,773
Parent Company
ASSETS
Cash and cash equivalents	85,365	120,016
Accounts receivable from affiliates	495	515
Current intercompany accounts receivable, net	0	1,255
Other current assets	20,648	10,448
Investment in subsidiaries	211,468	189,338
Property, plant and equipment, net	110	167
Other non-current assets	5,890	4,570
Total assets	323,976	326,309
LIABILITIES AND EQUITY
Current liabilities	3,242	5,257
Current intercompany accounts payable, net	2,337	0
Current portion of deferred compensation	0	13,465
Other long-term liabilities	1,023	1,245
Stockholders’ equity	300,624	289,392
Total liabilities and equity	323,976	326,309
Parent Company | Bellaire
LIABILITIES AND EQUITY
Note payable to Bellaire	$ 16,750	$ 16,950