Fair Value Measurements (Details 1) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Securities available‑for‑sale	$ 3,240,586	$ 3,559,437
Warrants Not Settleable in Cash, Fair Value Disclosure	5,033	4,914
Level 1
Securities available‑for‑sale		71,942
Level 2
Securities available‑for‑sale		3,388,054
Level 3
Securities available‑for‑sale		99,441
Government agency and government-sponsored enterprise pass through securities
Securities available‑for‑sale	653,865	767,797
Government agency and government-sponsored enterprise collateralized mortgage obligations
Securities available‑for‑sale	443,732	486,239
Covered private label collateralized mortgage obligation
Securities available‑for‑sale	27,863	29,782
Municipal securities
Securities available‑for‑sale	1,517,592	1,547,331
US Treasury Securities
Securities available‑for‑sale	0	69,380
Asset-backed Securities
Securities available‑for‑sale	202,674	211,157
Corporate Debt Securities
Securities available‑for‑sale	45,483	48,424
Collateralized Loan Obligations
Securities available‑for‑sale	139,572	132,189
US Government-sponsored Enterprises Debt Securities
Securities available‑for‑sale	0	36,913
Asset-backed and other securities
Securities available‑for‑sale	102,423	115,211
Fair Value, Measurements, Recurring
Securities available‑for‑sale	3,240,586	3,559,437
Derivative Asset, Fair Value of Collateral	6,654	11,919
Assets, Fair Value Disclosure, Recurring	3,252,273	3,576,270
Derivative Liability, Fair Value of Collateral	2,079	1,397
Fair Value, Measurements, Recurring | Level 1
Securities available‑for‑sale	2,551	71,942
Derivative Asset, Fair Value of Collateral	0	0
Warrants Not Settleable in Cash, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure, Recurring	2,551	71,942
Derivative Liability, Fair Value of Collateral	0	0
Fair Value, Measurements, Recurring | Level 2
Securities available‑for‑sale	3,146,104	3,388,054
Derivative Asset, Fair Value of Collateral	6,654	11,919
Warrants Not Settleable in Cash, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure, Recurring	3,152,758	3,399,973
Derivative Liability, Fair Value of Collateral	2,079	1,397
Fair Value, Measurements, Recurring | Level 3
Securities available‑for‑sale	91,931	99,441
Derivative Asset, Fair Value of Collateral	0	0
Warrants Not Settleable in Cash, Fair Value Disclosure	5,033	4,914
Assets, Fair Value Disclosure, Recurring	96,964	104,355
Derivative Liability, Fair Value of Collateral	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities
Securities available‑for‑sale		767,797
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities | Level 2
Securities available‑for‑sale	653,865	767,797
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations
Securities available‑for‑sale		486,239
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations | Level 2
Securities available‑for‑sale	443,732	486,239
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise collateralized mortgage obligations | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Covered private label collateralized mortgage obligation
Securities available‑for‑sale		29,782
Fair Value, Measurements, Recurring | Covered private label collateralized mortgage obligation | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Covered private label collateralized mortgage obligation | Level 2
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Covered private label collateralized mortgage obligation | Level 3
Securities available‑for‑sale	27,863	29,782
Fair Value, Measurements, Recurring | Other Private Label Collateralized Mortgage Obligations
Securities available‑for‑sale		115,014
Fair Value, Measurements, Recurring | Other Private Label Collateralized Mortgage Obligations | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Other Private Label Collateralized Mortgage Obligations | Level 2
Securities available‑for‑sale	60,030	63,555
Fair Value, Measurements, Recurring | Other Private Label Collateralized Mortgage Obligations | Level 3
Securities available‑for‑sale	47,352	51,459
Fair Value, Measurements, Recurring | Municipal securities
Securities available‑for‑sale		1,547,331
Fair Value, Measurements, Recurring | Municipal securities | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Municipal securities | Level 2
Securities available‑for‑sale	1,517,592	1,547,331
Fair Value, Measurements, Recurring | Municipal securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | US Treasury Securities | Level 1
Securities available‑for‑sale		69,380
Fair Value, Measurements, Recurring | US Treasury Securities | Level 2
Securities available‑for‑sale		0
Fair Value, Measurements, Recurring | US Treasury Securities | Level 3
Securities available‑for‑sale		0
Fair Value, Measurements, Recurring | Asset-backed Securities | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Asset-backed Securities | Level 2
Securities available‑for‑sale	202,674	211,157
Fair Value, Measurements, Recurring | Asset-backed Securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Corporate Debt Securities
Securities available‑for‑sale		48,424
Fair Value, Measurements, Recurring | Corporate Debt Securities | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Corporate Debt Securities | Level 2
Securities available‑for‑sale	45,483	48,424
Fair Value, Measurements, Recurring | Corporate Debt Securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Collateralized Loan Obligations | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Collateralized Loan Obligations | Level 2
Securities available‑for‑sale	139,572	132,189
Fair Value, Measurements, Recurring | Collateralized Loan Obligations | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | US Government-sponsored Enterprises Debt Securities
Securities available‑for‑sale		36,913
Fair Value, Measurements, Recurring | US Government-sponsored Enterprises Debt Securities | Level 1
Securities available‑for‑sale		0
Fair Value, Measurements, Recurring | US Government-sponsored Enterprises Debt Securities | Level 2
Securities available‑for‑sale		36,913
Fair Value, Measurements, Recurring | US Government-sponsored Enterprises Debt Securities | Level 3
Securities available‑for‑sale		0
Fair Value, Measurements, Recurring | Asset-backed and other securities
Securities available‑for‑sale		115,211
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 1
Securities available‑for‑sale	2,551	2,562
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 2
Securities available‑for‑sale	83,156	94,449
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 3
Securities available‑for‑sale	$ 16,716	$ 18,200