Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Securities available‑for‑sale	$ 3,336,992	$ 3,223,830
Equity warrants		5,497
Level 1
Securities available‑for‑sale		2,080
Level 2
Securities available‑for‑sale		3,156,475
Level 3
Securities available‑for‑sale		65,275
Government agency and government-sponsored enterprise pass through securities
Securities available‑for‑sale	474,556	502,443
Government agency and government-sponsored enterprise collateralized mortgage obligations
Securities available‑for‑sale	138,932	146,289
Municipal securities
Securities available‑for‑sale	1,483,281	1,456,459
Government agency and government-sponsored enterprise commercial mortgage-backed securities
Securities available‑for‑sale	712,071	547,692
Corporate debt securities
Securities available‑for‑sale	18,211	47,509
Collateralized loan obligations
Securities available‑for‑sale	127,973	156,887
SBA asset-backed securities
Securities available‑for‑sale	168,334	178,845
Asset-backed and other securities
Securities available‑for‑sale	64,234	62,237
Fair Value, Measurements, Recurring
Securities available‑for‑sale	3,336,992	3,223,830
Derivative assets	427	694
Equity warrants	5,368	5,497
Total recurring assets	3,342,787	3,230,021
Derivative liabilities	3,295	3,285
Fair Value, Measurements, Recurring | Level 1
Securities available‑for‑sale	1,960	2,080
Derivative assets	0	0
Equity warrants	0	0
Total recurring assets	1,960	2,080
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 2
Securities available‑for‑sale	3,281,875	3,156,475
Derivative assets	427	694
Equity warrants	0	0
Total recurring assets	3,282,302	3,157,169
Derivative liabilities	3,295	3,285
Fair Value, Measurements, Recurring | Level 3
Securities available‑for‑sale	53,157	65,275
Derivative assets	0	0
Equity warrants	5,368	5,497
Total recurring assets	58,525	70,772
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities
Securities available‑for‑sale	474,556	502,443
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	474,556	502,443
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	138,932	146,289
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	138,932	146,289
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 | Private Label Collateralized Mortgage Obligations
Securities available‑for‑sale	149,400	125,469
Fair Value, Measurements, Recurring | Private Label Collateralized Mortgage Obligations | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Private Label Collateralized Mortgage Obligations | Level 2
Securities available‑for‑sale	104,119	68,567
Fair Value, Measurements, Recurring | Private Label Collateralized Mortgage Obligations | Level 3
Securities available‑for‑sale	45,281	56,902
Fair Value, Measurements, Recurring | Municipal securities
Securities available‑for‑sale	1,483,281	1,456,459
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	1,483,281	1,456,459
Fair Value, Measurements, Recurring | Municipal securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities
Securities available‑for‑sale	712,071	547,692
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities | Level 2
Securities available‑for‑sale	712,071	547,692
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise commercial mortgage-backed securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Corporate debt securities
Securities available‑for‑sale	18,211	47,509
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	18,211	47,509
Fair Value, Measurements, Recurring | Corporate debt securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Collateralized loan obligations
Securities available‑for‑sale	127,973	156,887
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	127,973	156,887
Fair Value, Measurements, Recurring | Collateralized loan obligations | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | SBA asset-backed securities
Securities available‑for‑sale	168,334	178,845
Fair Value, Measurements, Recurring | SBA asset-backed securities | Level 1
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | SBA asset-backed securities | Level 2
Securities available‑for‑sale	168,334	178,845
Fair Value, Measurements, Recurring | SBA asset-backed securities | Level 3
Securities available‑for‑sale	0	0
Fair Value, Measurements, Recurring | Asset-backed and other securities
Securities available‑for‑sale	64,234	62,237
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 1
Securities available‑for‑sale	1,960	2,080
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 2
Securities available‑for‑sale	54,398	51,784
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 3
Securities available‑for‑sale	$ 7,876
Square 1 Financial, Inc. [Member] | Fair Value, Measurements, Recurring | Level 3
Equity warrants		5,497
Square 1 Financial, Inc. [Member] | Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 3
Securities available‑for‑sale		$ 8,373