Business Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) Segment	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments (segment) | Segment	2
Interest income	$ 107,639	$ 93,852	$ 204,604	$ 176,946
Interest expense	40,317	25,246	72,251	45,922
Net interest income	67,322	68,606	132,353	131,024
Provision for loan losses	(784)	535	1,333	3,585
Total non-interest income	16,127	18,391	37,037	41,144
Non-interest expense	53,750	50,413	106,031	99,778
Income before income tax expense	30,483	36,049	62,026	68,805
Income tax expense (benefit)	6,820	12,327	14,222	19,336
Net income (loss)	23,663	23,722	47,804	49,469
Preferred stock dividends	3,615	3,615	7,229	7,229
Net income (loss) available to common shareholders	20,048	20,107	40,575	42,240
Goodwill and other intangibles	17,150		17,150		$ 16,295
Assets	11,092,846		11,092,846		9,839,555
Deposits	7,295,954		7,295,954		$ 6,800,142
Combined Business Segments
Segment Reporting Information [Line Items]
Interest income	107,639	93,852	204,604	176,946
Interest expense	40,317	25,246	72,251	45,922
Net interest income	67,322	68,606	132,353	131,024
Provision for loan losses	(784)	535	1,333	3,585
Total non-interest income	16,127	18,391	37,037	41,144
Non-interest expense	53,750	50,413	106,031	99,778
Income before income tax expense	30,483	36,049	62,026	68,805
Income tax expense (benefit)	6,820	12,327	14,222	19,336
Net income (loss)	23,663	23,722	47,804	49,469
Preferred stock dividends	3,615	3,615	7,229	7,229
Net income (loss) available to common shareholders	20,048	20,107	40,575	42,240
Goodwill and other intangibles	17,150	17,615	17,150	17,615
Assets	11,092,846	10,883,548	11,092,846	10,883,548
Deposits	7,295,954	7,475,363	7,295,954	7,475,363
Non-deposit Liabilities	$ 2,860,665	$ 2,497,896	2,860,665	2,497,896
Operating Segments | Community Business Banking
Segment Reporting Information [Line Items]
Effective tax rate	24.57%	38.00%
Interest income	$ 104,110	$ 91,107	196,664	169,938
Interest expense	40,182	25,228	72,100	45,883
Net interest income	63,928	65,879	124,564	124,055
Provision for loan losses	(1,247)	535	627	3,585
Total non-interest income	7,465	6,971	15,904	12,398
Non-interest expense	37,721	30,567	72,052	60,714
Income before income tax expense	34,919	41,748	67,789	72,154
Income tax expense (benefit)	7,910	14,493	15,638	20,609
Net income (loss)	27,009	27,255	52,151	51,545
Preferred stock dividends	3,615	3,615	7,229	7,229
Net income (loss) available to common shareholders	23,394	23,640	44,922	44,316
Goodwill and other intangibles	3,629	3,633	3,629	3,633
Assets	11,017,272	10,815,752	11,017,272	10,815,752
Deposits	6,876,688	7,021,922	6,876,688	7,021,922
Non-deposit Liabilities	2,843,360	2,481,618	2,843,360	2,481,618
Operating Segments | BankMobile
Segment Reporting Information [Line Items]
Interest income	3,529	2,745	7,940	7,008
Interest expense	135	18	151	39
Net interest income	3,394	2,727	7,789	6,969
Provision for loan losses	463	0	706	0
Total non-interest income	8,662	11,420	21,133	28,746
Non-interest expense	16,029	19,846	33,979	39,064
Income before income tax expense	(4,436)	(5,699)	(5,763)	(3,349)
Income tax expense (benefit)	(1,090)	(2,166)	(1,416)	(1,273)
Net income (loss)	(3,346)	(3,533)	(4,347)	(2,076)
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	(3,346)	(3,533)	(4,347)	(2,076)
Goodwill and other intangibles	13,521	13,982	13,521	13,982
Assets	75,574	67,796	75,574	67,796
Deposits	419,266	453,441	419,266	453,441
Non-deposit Liabilities	17,305	16,278	17,305	16,278
Segment Reconciling Items | BankMobile
Segment Reporting Information [Line Items]
Interest income	$ 3,500	$ 2,700	$ 7,900	$ 7,000