Condensed Consolidated Statements of Changes in Shareholders’ Equity (USD $) In Thousands	Total	Common Stock	Common Stock Subscribed, Unissued	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at Dec. 31, 2009	$ 538,169	$ 211,970	$ 0	$ 423,920	$ (102,599)	$ 4,878
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	33,057			32,877		180
Foreign currency translation	1,063				1,020	43
Unrealized gain (loss) from interest rate swap (net of tax)	(207)				(207)
Pension and postretirement benefits liability adjustment (net of tax)	6,402				6,402
Comprehensive income	40,315
Stock issued	7,933	7,933
Stock purchased	(8,179)	(8,069)				(110)
Advance payments	644		644
Dividends declared	(9,550)			(9,550)
Balance at Sep. 30, 2010	569,332	211,834	644	447,247	(95,384)	4,991
Balance at Dec. 31, 2010	558,807	232,400	0	423,602	(102,343)	5,148
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	68,340			67,995		345
Foreign currency translation	(2,383)				(2,304)	(79)
Unrealized gain (loss) from interest rate swap (net of tax)	612				612
Pension and postretirement benefits liability adjustment (net of tax)	7,010				7,010
Comprehensive income	73,579
Stock issued	9,878
Stock Issued During Period, Value, New Issues		9,366				512
Stock purchased	(7,444)	(7,340)				(104)
Advance payments	379		379
Dividends declared	(10,572)			(10,572)
Balance at Sep. 30, 2011	$ 624,627	$ 234,426	$ 379	$ 481,025	$ (97,025)	$ 5,822