Condensed Financial Information (Parent Company Only) - Condensed Statements of Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions
Salaries and benefits	$ 89,833	$ 83,560	$ 83,373
Interest expense	30,114	42,031	63,107
Earnings before income tax benefit	88,262	66,161	54,446
Income tax benefit	30,038	21,615	17,090
Net income	58,224	44,546	37,356
Parent Company
Condensed Financial Statements, Captions
Dividends from subsidiaries	40,000	30,000	15,400
Other interest income	92	118	105
Other income, primarily management fees from subsidiaries	10,042	10,617	11,336
Total income	50,134	40,735	26,841
Salaries and benefits	13,205	13,975	13,435
Interest expense	6,691	7,273	7,703
Other operating expenses, net	7,150	6,903	6,827
Total expenses	27,046	28,151	27,965
Earnings before income tax benefit	23,088	12,584	(1,124)
Income tax benefit	(6,222)	(6,518)	(6,254)
Income before undistributed earnings of subsidiaries	29,310	19,102	5,130
Undistributed earnings of subsidiaries	28,914	25,444	32,226
Net income	$ 58,224	$ 44,546	$ 37,356