Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Securities available‑for‑sale	$ 3,223,830	$ 3,559,437
Warrants Not Settleable in Cash, Fair Value Disclosure		4,914
Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	3,223,830	3,559,437
Derivative Asset, Fair Value of Collateral	694	11,919
Warrants Not Settleable in Cash, Fair Value Disclosure		4,914
Assets, Fair Value Disclosure, Recurring	3,230,021	3,576,270
Derivative Liability, Fair Value of Collateral	3,285	1,397
Level 1
Securities available‑for‑sale		71,942
Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	2,080	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	2,080	71,942
Derivative Liability, Fair Value of Collateral	0	0
Level 2
Securities available‑for‑sale		3,388,054
Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	3,156,475	3,388,054
Derivative Asset, Fair Value of Collateral	694	11,919
Warrants Not Settleable in Cash, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure, Recurring	3,157,169	3,399,973
Derivative Liability, Fair Value of Collateral	3,285	1,397
Level 3
Securities available‑for‑sale		99,441
Warrants Not Settleable in Cash, Fair Value Disclosure		4,914
Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	65,275	99,441
Derivative Asset, Fair Value of Collateral	0	0
Warrants Not Settleable in Cash, Fair Value Disclosure	5,497	4,914
Assets, Fair Value Disclosure, Recurring	70,772	104,355
Derivative Liability, Fair Value of Collateral	0	0
Level 3 | Fair Value, Measurements, Recurring [Member] | Square 1 Financial, Inc. [Member]
Warrants Not Settleable in Cash, Fair Value Disclosure		4,914
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	502,443	667,840
Government agency and government-sponsored enterprise pass through securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Government agency and government-sponsored enterprise pass through securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	502,443	667,840
Government agency and government-sponsored enterprise pass through securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	146,289	194,755
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	146,289	194,755
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Private Label Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	125,469	144,796
Private Label Collateralized Mortgage Obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Private Label Collateralized Mortgage Obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	68,567	63,555
Private Label Collateralized Mortgage Obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	56,902	81,241
Private Label Collateralized Mortgage Obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member] | Square 1 Financial, Inc. [Member]
Securities available‑for‑sale		51,500
Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	1,456,459	1,547,331
Municipal Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Municipal Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	1,456,459	1,547,331
Municipal Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	547,692	391,441
Commercial Mortgage Backed Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Commercial Mortgage Backed Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	547,692	391,441
Commercial Mortgage Backed Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	47,509	48,424
Corporate Debt Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Corporate Debt Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	47,509	48,424
Corporate Debt Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Collateralized Loan Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	156,887	132,189
Collateralized Loan Obligations [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Collateralized Loan Obligations [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	156,887	132,189
Collateralized Loan Obligations [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
SBA asset-backed securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	178,845	211,157
SBA asset-backed securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
SBA asset-backed securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	178,845	211,157
SBA asset-backed securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	0	0
Asset-backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	62,237	115,211
Asset-backed Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	2,080	2,562
Asset-backed Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	51,784	94,449
Asset-backed Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale	8,373
Asset-backed Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member] | Square 1 Financial, Inc. [Member]
Securities available‑for‑sale		18,200
US Treasury Securities [Member]
Securities available‑for‑sale	0	69,380
US Treasury Securities [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		69,380
US Treasury Securities [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		0
US Treasury 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	$ 0	36,913
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		36,913
US Government-sponsored Enterprises Debt Securities [Member] | Level 3 | Fair Value, Measurements, Recurring [Member]
Securities available‑for‑sale		$ 0