Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Securities available‑for‑sale	$ 1,539,681	$ 1,494,745
Level 1
Securities available‑for‑sale	514	507
Level 2
Securities available‑for‑sale	1,503,858	1,456,334
Level 3
Securities available‑for‑sale	35,309	37,904
Government agency and government-sponsored enterprise pass through securities
Securities available‑for‑sale		707,188
Government agency and government-sponsored enterprise pass through securities | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	555,087
Government agency and government-sponsored enterprise pass through securities | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Government agency and government-sponsored enterprise pass through securities | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	555,087
Government agency and government-sponsored enterprise pass through securities | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Securities available‑for‑sale		192,873
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	279,791
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	279,791
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Covered private label collateralized mortgage obligation [Member]
Securities available‑for‑sale		37,904
Covered private label collateralized mortgage obligation [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	35,309
Covered private label collateralized mortgage obligation [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Covered private label collateralized mortgage obligation [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Covered private label collateralized mortgage obligation [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	35,309
Other Private Label Collateralized Mortgage Obligations [Member]
Securities available‑for‑sale		0
Other Private Label Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	12,593
Other Private Label Collateralized Mortgage Obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Other Private Label Collateralized Mortgage Obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	12,593
Other Private Label Collateralized Mortgage Obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Municipal securities
Securities available‑for‑sale		436,658
Municipal securities | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	482,427
Municipal securities | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Municipal securities | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	482,427
Municipal securities | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Corporate Debt Securities [Member]
Securities available‑for‑sale		82,707
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	112,143
Corporate Debt Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Corporate Debt Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	112,143
Corporate Debt Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
US Government-sponsored Enterprises Debt Securities [Member]
Securities available‑for‑sale		9,872
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	36,382
US Government-sponsored Enterprises Debt Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
US Government-sponsored Enterprises Debt Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	36,382
US Government-sponsored Enterprises Debt Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0
Other securities [Member]
Securities available‑for‑sale		27,543
Other securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	25,949
Other securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	514
Other securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	25,435
Other securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	$ 0