Investment Securities - Gross Unrealized Losses and Fair Values of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013 securities	Dec. 31, 2012 securities
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	$ 1,092,584	$ 344,180
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(27,628)	(1,689)
Available-for-Sale, 12 months or more fair value	226,396	137
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(9,769)	(1)
Available-for-Sale, total fair value	1,318,980	344,317
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(37,397)	(1,690)
Held-to-Maturity:
Held-to-maturity, less than 12 months fair value	44,844	28,701
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(1,327)	(181)
Held-to-maturity, 12 months or more fair value	14,296	557
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(730)	(8)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	59,140	29,258
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(2,057)	(189)
Available-for-Sale and Held-to-Maturity:
Investment securities in an unrealized loss position (number of securities)	229	69
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	458,385	93,982
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(10,355)	(163)
Available-for-Sale, 12 months or more fair value	59,362	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(1,894)	0
Available-for-Sale, total fair value	517,747	93,982
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(12,249)	(163)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	634,199	250,198
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(17,273)	(1,526)
Available-for-Sale, 12 months or more fair value	166,930	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(7,874)	0
Available-for-Sale, total fair value	801,129	250,198
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(25,147)	(1,526)
Private mortgage-backed securities
Available-for-Sale:
Available-for-Sale, less than 12 months fair value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	0	0
Available-for-Sale, 12 months or more fair value	104	137
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(1)	(1)
Available-for-Sale, total fair value	104	137
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(1)	(1)
State, county and municipal securities
Held-to-Maturity:
Held-to-maturity, less than 12 months fair value	37,550	19,389
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(1,319)	(168)
Held-to-maturity, 12 months or more fair value	14,296	557
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(730)	(8)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	51,846	19,946
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(2,049)	(176)
Corporate securities
Held-to-Maturity:
Held-to-maturity, less than 12 months fair value	7,294	9,312
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(8)	(13)
Held-to-maturity, 12 months or more fair value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	7,294	9,312
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	$ (8)	$ (13)