Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Securities available‑for‑sale	$ 3,474,560	$ 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	404,320	502,443
Government agency and government-sponsored enterprise collateralized mortgage obligations
Securities available‑for‑sale	133,792	146,289
Municipal securities
Securities available‑for‑sale	1,534,554	1,456,459
Government agency and government-sponsored enterprise commercial mortgage-backed securities
Securities available‑for‑sale	918,210	547,692
Corporate debt securities
Securities available‑for‑sale	19,185	47,509
Collateralized loan obligations
Securities available‑for‑sale	66,301	156,887
SBA asset-backed securities
Securities available‑for‑sale	178,056	178,845
Asset-backed and other securities
Securities available‑for‑sale	60,441	62,237
Fair Value, Measurements, Recurring
Securities available‑for‑sale	3,474,560	3,223,830
Other derivative assets	235	694
Equity warrants	5,452	5,497
Total recurring assets	3,480,247	3,230,021
Derivative liabilities	2,235	3,285
Fair Value, Measurements, Recurring | Level 1
Securities available‑for‑sale	3,721	2,080
Other derivative assets	0	0
Equity warrants	0	0
Total recurring assets	3,721	2,080
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 2
Securities available‑for‑sale	3,404,537	3,156,475
Other derivative assets	235	694
Equity warrants	0	0
Total recurring assets	3,404,772	3,157,169
Derivative liabilities	2,235	3,285
Fair Value, Measurements, Recurring | Level 3
Securities available‑for‑sale	66,302	65,275
Other derivative assets	0	0
Equity warrants	5,452	5,497
Total recurring assets	71,754	70,772
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Government agency and government-sponsored enterprise pass through securities
Securities available‑for‑sale	404,320	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	404,320	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	133,792	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	133,792	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	159,701	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	100,162	68,567
Fair Value, Measurements, Recurring | Private Label Collateralized Mortgage Obligations | Level 3
Securities available‑for‑sale	59,539	56,902
Fair Value, Measurements, Recurring | Municipal securities
Securities available‑for‑sale	1,534,554	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	1,534,554	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	918,210	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	918,210	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	19,185	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	19,185	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	66,301	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	66,301	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	178,056	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	178,056	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	60,441	62,237
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 1
Securities available‑for‑sale	3,721	2,080
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 2
Securities available‑for‑sale	49,957	51,784
Fair Value, Measurements, Recurring | Asset-backed and other securities | Level 3
Securities available‑for‑sale	$ 6,763
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