Parent Company Only Condensed Financial Statements - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash	$ 153,323	$ 198,802	$ 94,157	$ 100,696
Total assets	5,289,225	4,081,328
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	118,105	105,540
Shareholders' equity	548,573	387,098	350,829	316,241
Total liabilities and shareholders' equity	5,289,225	4,081,328
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	9,977	52,245	$ 12,032	$ 14,532
Other assets	28,741	22,111
Total assets	668,703	493,985
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	118,105	105,540
Accounts payable and other liabilities	2,025	1,347
Shareholders' equity	548,573	387,098
Total liabilities and shareholders' equity	668,703	493,985
Enterprise Bank and Trust [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	623,439	416,831
Nonbank Subsidiaries [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	$ 6,546	$ 2,798