Consolidated Statements of Changes in Shareholders’ Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at Dec. 31, 2008	$ 507,591	$ 193,256	$ 425,276	$ (114,869)	$ 3,928
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	37,442		37,277		165
Other comprehensive income (loss)	12,700			12,270	430
Stock issued	11,856	11,392			464
Stock purchased	(12,010)	(11,901)			(109)
Dividends declared	(19,410)	19,223	(38,633)
Balance at Dec. 31, 2009	538,169	211,970	423,920	(102,599)	4,878
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	42,293		41,998		295
Other comprehensive income (loss)	382			256	126
Stock issued	9,799	9,799
Stock purchased	(10,599)	(10,448)			(151)
Dividends declared	(21,237)	21,079	(42,316)
Balance at Dec. 31, 2010	558,807	232,400	423,602	(102,343)	5,148
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	81,891		81,425		466
Other comprehensive income (loss)	(48,049)			(48,021)	(28)
Stock issued	11,633	11,121			512
Stock purchased	(9,373)	(9,264)			(109)
Dividends declared	(23,515)	23,373	(46,888)
Balance at Dec. 31, 2011	$ 571,394	$ 257,630	$ 458,139	$ (150,364)	$ 5,989