Loans and the Allowance for Credit Losses (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of age analysis of loan categories
Current	$ 3,634,126	$ 3,629,661
30-59 Days Past Due	12,795	17,713
60-89 Days Past Due	7,584	8,789
90 Days or More Past Due	29,296	31,599
Total Past Due	49,675	58,101
Total Loans	3,683,801	3,687,762
90 Days or More Past Due and Accruing	4,345	5,294
Loans held for sale	14,299	21,903
Total loans, current	3,648,425	3,651,564
Total loans	3,698,100	3,709,665
Commercial real estate land and construction [Member]
Summary of age analysis of loan categories
Current	181,026	189,072
30-59 Days Past Due	264	1,470
60-89 Days Past Due
90 Days or More Past Due	3,512	2,462
Total Past Due	3,776	3,932
Total Loans	184,802	193,004
90 Days or More Past Due and Accruing
Commercial real estate improved property [Member]
Summary of age analysis of loan categories
Current	1,627,755	1,643,833
30-59 Days Past Due	2,573	5,722
60-89 Days Past Due	4,067	2,224
90 Days or More Past Due	12,557	13,562
Total Past Due	19,197	21,508
Total Loans	1,646,952	1,665,341
90 Days or More Past Due and Accruing	625	338
Commercial real estate [Member]
Summary of age analysis of loan categories
Current	1,808,781	1,832,905
30-59 Days Past Due	2,837	7,192
60-89 Days Past Due	4,067	2,224
90 Days or More Past Due	16,069	16,024
Total Past Due	22,973	25,440
Total Loans	1,831,754	1,858,345
90 Days or More Past Due and Accruing	625	338
Commercial and industrial [Member]
Summary of age analysis of loan categories
Current	492,605	475,186
30-59 Days Past Due	864	283
60-89 Days Past Due	443	412
90 Days or More Past Due	1,836	2,144
Total Past Due	3,143	2,839
Total Loans	495,748	478,025
90 Days or More Past Due and Accruing	86	98
Residential real estate [Member]
Summary of age analysis of loan categories
Current	792,086	774,006
30-59 Days Past Due	4,555	4,231
60-89 Days Past Due	2,296	4,833
90 Days or More Past Due	9,591	10,632
Total Past Due	16,442	19,696
Total Loans	808,528	793,702
90 Days or More Past Due and Accruing	2,666	3,199
Home equity [Member]
Summary of age analysis of loan categories
Current	275,812	274,235
30-59 Days Past Due	1,652	1,352
60-89 Days Past Due	209	197
90 Days or More Past Due	1,139	1,442
Total Past Due	3,000	2,991
Total Loans	278,812	277,226
90 Days or More Past Due and Accruing	482	722
Consumer [Member]
Summary of age analysis of loan categories
Current	264,842	273,329
30-59 Days Past Due	2,887	4,655
60-89 Days Past Due	569	1,123
90 Days or More Past Due	661	1,357
Total Past Due	4,117	7,135
Total Loans	268,959	280,464
90 Days or More Past Due and Accruing	486	937
Loans held for sale [Member]
Summary of age analysis of loan categories
30-59 Days Past Due
60-89 Days Past Due
90 Days or More Past Due
Total Past Due
90 Days or More Past Due and Accruing
Loans held for sale, current	14,299	21,903
Loans held for sale	14,299	21,903
Nonaccrual loans [Member]
Summary of age analysis of loan categories
Current	12,949	11,724
30-59 Days Past Due	1,160	591
60-89 Days Past Due	4,180	1,747
90 Days or More Past Due	24,437	25,310
Total Past Due	29,777	27,648
Total Loans	42,726	39,372
TDRS [Member]
Summary of age analysis of loan categories
Current	19,374	21,665
30-59 Days Past Due	487	794
60-89 Days Past Due	45	827
90 Days or More Past Due	514	995
Total Past Due	1,046	2,616
Total Loans	$ 20,420	$ 24,281