Investment Securities, Available-for-Sale (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Total investment securities, weighted yield	2.88%	2.71%
Total investment securities, amortized cost	$ 3,681,838	$ 3,587,677
Total investment securities, gross unrealized gains	65,574	101,778
Total investment securities, gross unrealized losses	(26,035)	(6,450)
Total investment securities, fair value	3,721,377	3,683,005
U.S. government and federal agency [Member]
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing within one year, weighted yield		1.62%
Maturing within one year, amortized cost		201
Maturing within one year, gross unrealized gains		1
Maturing within one year, fair value		202
U.S. government sponsored enterprises [Member]
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing after one year through five years, weighted yield	2.27%	2.30%
Maturing after five years through ten years, weighted yield	1.71%	2.03%
Total investment securities, weighted yield	2.27%	2.29%
Maturing after one year through five years, amortized cost	12,840	17,064
Maturing after five years through ten years, amortized cost	40	44
Total investment securities, amortized cost	12,880	17,108
Maturing after one year through five years, gross unrealized gains	270	371
Maturing after five years through ten years, gross unrealized gains	1	1
Total investment securities, gross unrealized gains	271	372
Maturing after one year through five years, fair value	13,110	17,435
Maturing after five years through ten years, fair value	41	45
Total investment securities, fair value	13,151	17,480
State and local governments [Member]
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing within one year, weighted yield	2.02%	2.01%
Maturing after one year through five years, weighted yield	2.07%	2.11%
Maturing after five years through ten years, weighted yield	3.11%	2.95%
Maturing after ten years, weighted yield	4.53%	4.70%
Total investment securities, weighted yield	4.17%	4.29%
Maturing within one year, amortized cost	5,066	4,288
Maturing after one year through five years, amortized cost	158,331	149,497
Maturing after five years through ten years, amortized cost	55,026	38,346
Maturing after ten years, amortized cost	1,089,519	935,897
Total investment securities, amortized cost	1,307,942	1,128,028
Maturing within one year, gross unrealized gains	41	28
Maturing after one year through five years, gross unrealized gains	3,063	4,142
Maturing after five years through ten years, gross unrealized gains	904	1,102
Maturing after ten years, gross unrealized gains	44,313	82,823
Total investment securities, gross unrealized gains	48,321	88,095
Maturing within one year, gross unrealized losses	0	(2)
Maturing after one year through five years, gross unrealized losses	(265)	(142)
Maturing after five years through ten years, gross unrealized losses	(656)	(99)
Maturing after ten years, gross unrealized losses	(15,466)	(1,362)
Total investment securities, gross unrealized losses	(16,387)	(1,605)
Maturing within one year, fair value	5,107	4,314
Maturing after one year through five years, fair value	161,129	153,497
Maturing after five years through ten years, fair value	55,274	39,349
Maturing after ten years, fair value	1,118,366	1,017,358
Total investment securities, fair value	1,339,876	1,214,518
Corporate bonds [Member]
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing within one year, weighted yield	2.06%	1.73%
Maturing after one year through five years, weighted yield	2.10%	2.22%
Maturing after five years through ten years, weighted yield	2.27%	2.23%
Total investment securities, weighted yield	2.10%	2.19%
Maturing within one year, amortized cost	64,391	18,412
Maturing after one year through five years, amortized cost	357,036	250,027
Maturing after five years through ten years, amortized cost	21,635	16,144
Total investment securities, amortized cost	443,062	284,583
Maturing within one year, gross unrealized gains	630	51
Maturing after one year through five years, gross unrealized gains	2,571	4,018
Maturing after five years through ten years, gross unrealized gains	53	381
Total investment securities, gross unrealized gains	3,254	4,450
Maturing within one year, gross unrealized losses	0	0
Maturing after one year through five years, gross unrealized losses	(3,173)	(238)
Maturing after five years through ten years, gross unrealized losses	(346)
Total investment securities, gross unrealized losses	(3,519)	(238)
Maturing within one year, fair value	65,021	18,463
Maturing after one year through five years, fair value	356,434	253,807
Maturing after five years through ten years, fair value	21,342	16,525
Total investment securities, fair value	442,797	288,795
Collateralized debt obligations [Member]
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing after ten years, weighted yield		8.03%
Maturing after ten years, amortized cost		1,708
Maturing after ten years, gross unrealized losses		0
Maturing after ten years, fair value		1,708
Residential mortgage-backed securities [Member]
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Total investment securities, weighted yield	2.18%	1.95%
Total investment securities, amortized cost	1,917,954	2,156,049
Total investment securities, gross unrealized gains	13,728	8,860
Total investment securities, gross unrealized losses	(6,129)	(4,607)
Total investment securities, fair value	$ 1,925,553	$ 2,160,302