Fair Value Measurements (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 3,774,431,000	$ 3,223,830,000
Warrants Not Settleable in Cash, Fair Value Disclosure		5,497,000
Threshold for loans that are considered individually significant for allowance analysis purposes		250,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value		65,275,000
Warrants Not Settleable in Cash, Fair Value Disclosure		5,497,000	$ 4,914,000
Equity Warrants Transfers to Available For Sale Securities		836,000	(2,000)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	3,774,431,000	3,223,830,000
Warrants Not Settleable in Cash, Fair Value Disclosure	5,161,000	5,497,000
Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	64,983,000	65,275,000
Warrants Not Settleable in Cash, Fair Value Disclosure	5,161,000	5,497,000
Covered Private Label Collateralized Mortgage Obligations Member [Domain] | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	574,000	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	21,165,000	0	$ 0
Private Label Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	125,987,000	125,469,000
Other securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	95,780,000	62,237,000
Other securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	42,109,000
Warrant [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ (1,182,000)
Square 1 Financial, Inc. [Member] | Other securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value		$ 8,373,000