Schedule I - Condensed Financial Information of the Parent (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Activities
Net cash (used for) provided by operating activities	$ (2,486)	$ 52,784
Investing Activities
Expenditures for property, plant and equipment	(30,187)	(24,664)
Net cash used for investing activities	(45,984)	(20,262)
Financing Activities
Purchase of treasury shares	(1,002)	(3,010)
Cash dividends paid	(5,375)	(5,132)
Other	332	(3)
Net cash provided by financing activities	14,028	5,113
Cash and Cash Equivalents
Total (decrease) increase for the year	(34,442)	37,635
Balance at the beginning of the year	122,892	85,257
Balance at the end of the year	88,450	122,892
Parent Company
Operating Activities
Net income	14,793	39,632
Equity in earnings of subsidiaries	23,045	41,610
Net loss before equity in earnings of subsidiaries	(8,252)	(1,978)
Net changes related to operating activities	(22,822)	3,671
Net cash (used for) provided by operating activities	(31,074)	1,693
Investing Activities
Expenditures for property, plant and equipment	0	0
Net cash used for investing activities	0	0
Financing Activities
Dividends received from subsidiaries	3,000	42,000
Notes payable to Bellaire	(200)	(350)
Purchase of treasury shares	(1,002)	(3,010)
Cash dividends paid	(5,375)	(5,132)
Other	0	(4)
Net cash provided by financing activities	(3,577)	33,504
Cash and Cash Equivalents
Total (decrease) increase for the year	(34,651)	35,197
Balance at the beginning of the year	120,016	84,819
Balance at the end of the year	$ 85,365	$ 120,016