Schedule I - Condensed Financial Information of the Parent (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net cash provided by operating activities	$ 108,002	$ 19,799	$ 53,065
Investing Activities
Expenditures for property, plant and equipment	(10,615)	(57,500)	(57,449)
Net cash used for investing activities	(8,291)	(74,934)	(60,734)
Financing Activities
Purchase of treasury shares	(24,010)	(35,075)	(31,306)
Cash dividends paid	(7,296)	(7,755)	(8,104)
Other	922	(5)	(8)
Net cash provided by (used for) financing activities	(108,301)	20,979	(36,776)
Cash and cash equivalents
Decrease for the year	(8,636)	(34,255)	(44,465)
Balance at the beginning of the year	61,135	95,390	139,855
Balance at the end of the year	52,499	61,135	95,390
Parent Company
Operating Activities
Net income (loss)	21,984	(38,118)	44,450
Equity in earnings of subsidiaries	25,231	(33,991)	49,553
Parent company only net loss	3,247	4,127	5,103
Net changes related to operating activities	(11,015)	5,710	(1,858)
Net cash provided by operating activities	(14,262)	1,583	(6,961)
Investing Activities
Expenditures for property, plant and equipment	(328)	(103)	(238)
Net cash used for investing activities	(328)	(103)	(238)
Financing Activities
Cash dividends received from subsidiaries	15,000	22,300	20,000
Notes payable to Bellaire	0	(1,750)	0
Capital contributions to subsidiaries	0	(19,800)	0
Purchase of treasury shares	(24,010)	(35,075)	(31,306)
Cash dividends paid	(7,296)	(7,755)	(8,104)
Other	(13)	(20)	(15)
Net cash provided by (used for) financing activities	(16,319)	(42,100)	(19,425)
Cash and cash equivalents
Decrease for the year	(30,909)	(40,620)	(26,624)
Balance at the beginning of the year	53,415	94,035	120,659
Balance at the end of the year	$ 22,506	$ 53,415	$ 94,035