Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Consolidated Statements of Changes in Shareholders' Equity (Unaudited) [Abstract]
Balance, January 1,	$ 1,287,369	$ 1,215,037
Net income per consolidated statements of income	24,866	30,320
Other comprehensive income (loss)	2,314	(1,584)
Common stock dividends paid	(15,560)	(14,900)
Common stock issued-net, long-term incentive plans:
Stock options	109	33
Restricted stock	(938)	(1,187)
Excess tax benefit from stock-based compensation arrangements	269	674
Compensation expense, long-term incentive plan	1,022	1,127
Common stock issued, business combination	53,495	12,000
Balance, End of Period	$ 1,352,946	$ 1,241,520