Segment Reporting (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets of company's reportable segments
Total Assets	$ 3,579,756	$ 3,328,005
Western [Member]
Assets of company's reportable segments
Total Assets	1,503,572	1,370,098
Central [Member]
Assets of company's reportable segments
Total Assets	1,051,871	1,040,962
Eastern [Member]
Assets of company's reportable segments
Total Assets	834,764	841,251
Corporate [Member]
Assets of company's reportable segments
Total Assets	$ 189,549	$ 75,694