Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statements of Changes in Shareholders' Equity (Unaudited) [Abstract]
Balance	$ 1,215,037	$ 1,149,484
Net income per consolidated statements of income	30,320	24,013
Other comprehensive income	(1,584)	(197)
Common stock dividends paid	(14,900)	(14,866)
Common stock issued-net, long-term incentive plans:
Stock options	33	401
Restricted stock	(1,187)	(620)
Excess tax benefit from stock-based compensation arrangements	674	976
Compensation expense, long-term incentive plans	1,127	1,038
Common stock issued, business combinations	12,000	0
Balance	$ 1,241,520	$ 1,160,229