Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Carrying Amount [Member]
Investment securities:
Available-for-sale	$ 4,755	$ 4,755	$ 0
Nonmarketable equity securities	25,572	25,572	25,572
Carrying Amount [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	578,726	656,135	473,678
Carrying Amount [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	698,867	582,054	676,007
Held-to-maturity	257,749	229,977	183,297
Loans Held-for-sale	14,850	17,665	25,080
Interest receivable	16,960	14,933	16,804
Liabilities:
Deposits without defined maturities	3,574,832	3,448,886	2,981,632
Interest payable	1,338	1,501	2,039
Short-term borrowings	347,484	310,463	335,082
FHLB advances	0	34,289	42,120
Carrying Amount [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	0	0	8,000
Net loans	4,102,427	4,083,244	3,755,313
Liabilities:
Time deposits	1,432,526	1,472,557	1,479,752
Fair Value [Member]
Investment securities:
Available-for-sale	4,755	4,755	0
Nonmarketable equity securities	25,572	25,572	25,572
Fair Value [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	578,726	656,135	473,678
Fair Value [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	698,867	582,054	676,007
Held-to-maturity	261,405	229,922	184,372
Loans Held-for-sale	14,850	17,665	25,109
Interest receivable	16,960	14,933	16,804
Liabilities:
Deposits without defined maturities	3,574,832	3,448,886	2,981,632
Interest payable	1,338	1,501	2,039
Short-term borrowings	347,484	310,463	335,082
FHLB advances	0	34,835	43,186
Fair Value [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	0	0	8,000
Net loans	4,123,585	4,093,880	3,781,585
Liabilities:
Time deposits	$ 1,448,634	$ 1,489,072	$ 1,500,227