Fair Value of Financial Instruments - Hierarchy Table - Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Disclosures
Investment securities available-for-sale, at fair value	$ 703,944	$ 380,963
Agency
Fair Value Disclosures
Investment securities available-for-sale, at fair value	50,379
Corporate
Fair Value Disclosures
Investment securities available-for-sale, at fair value	62,175	37,642
Municipal bonds
Fair Value Disclosures
Investment securities available-for-sale, at fair value	228,427	118,803
Collateralized mortgage obligation: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	43,404	31,388
Mortgage-backed securities: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	319,559	193,130
Level 1
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Level 2
Fair Value Disclosures
Investment securities available-for-sale, at fair value	703,944	380,963
Level 3
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis
Fair Value Disclosures
Investment securities available-for-sale, at fair value	703,944	380,963
Recurring basis | Agency
Fair Value Disclosures
Investment securities available-for-sale, at fair value	50,379
Recurring basis | Corporate
Fair Value Disclosures
Investment securities available-for-sale, at fair value	62,175	37,642
Recurring basis | Municipal bonds
Fair Value Disclosures
Investment securities available-for-sale, at fair value	228,427	118,803
Recurring basis | Collateralized mortgage obligation: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	43,404	31,388
Recurring basis | Mortgage-backed securities: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	319,559	193,130
Recurring basis | Level 1
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Agency
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0
Recurring basis | Level 1 | Corporate
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Municipal bonds
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Collateralized mortgage obligation: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Mortgage-backed securities: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 2
Fair Value Disclosures
Investment securities available-for-sale, at fair value	703,944	380,963
Recurring basis | Level 2 | Agency
Fair Value Disclosures
Investment securities available-for-sale, at fair value	50,379
Recurring basis | Level 2 | Corporate
Fair Value Disclosures
Investment securities available-for-sale, at fair value	62,175	37,642
Recurring basis | Level 2 | Municipal bonds
Fair Value Disclosures
Investment securities available-for-sale, at fair value	228,427	118,803
Recurring basis | Level 2 | Collateralized mortgage obligation: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	43,404	31,388
Recurring basis | Level 2 | Mortgage-backed securities: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	319,559	193,130
Recurring basis | Level 3
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Agency
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0
Recurring basis | Level 3 | Corporate
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Municipal bonds
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Collateralized mortgage obligation: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Mortgage-backed securities: residential
Fair Value Disclosures
Investment securities available-for-sale, at fair value	$ 0	$ 0