Investment Securities - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available for sale:
Total	$ 699,753	$ 385,662
Unrealized Gain	7,132	804
Unrealized Loss	(2,941)	(5,503)
Investment securities available-for-sale, at fair value	703,944	380,963
Held to maturity:
Amortized Cost	18,627	8,565
Unrealized Gain	0	0
Unrealized Loss	(50)	(104)
Estimated Fair Value	18,577	8,461
Total investment securities
Amortized Cost	718,380	394,227
Unrealized Gain	7,132	804
Unrealized Loss	2,991	5,607
Estimated Fair Value	722,521	389,424
Agency
Available for sale:
Total	49,969
Unrealized Gain	433
Unrealized Loss	(23)
Investment securities available-for-sale, at fair value	50,379
Corporate
Available for sale:
Total	61,040	37,475
Unrealized Gain	1,275	372
Unrealized Loss	(140)	(205)
Investment securities available-for-sale, at fair value	62,175	37,642
Municipal bonds
Available for sale:
Total	224,332	120,155
Unrealized Gain	4,481	338
Unrealized Loss	(386)	(1,690)
Investment securities available-for-sale, at fair value	228,427	118,803
Collateralized mortgage obligation: residential
Available for sale:
Total	43,254	31,536
Unrealized Gain	255	25
Unrealized Loss	(105)	(173)
Investment securities available-for-sale, at fair value	43,404	31,388
Mortgage-backed securities: residential
Available for sale:
Total	321,158	196,496
Unrealized Gain	688	69
Unrealized Loss	(2,287)	(3,435)
Investment securities available-for-sale, at fair value	319,559	193,130
Held to maturity:
Amortized Cost	17,476	7,375
Unrealized Gain	0	0
Unrealized Loss	(50)	(104)
Estimated Fair Value	17,426	7,271
Other
Held to maturity:
Amortized Cost	1,151	1,190
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	$ 1,151	$ 1,190