Fair Value Measurements - Estimated Fair Values and Related Carrying Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial assets:
Securities held to maturity	$ 16,416	$ 9,293
Carrying Amount
Financial assets:
Cash and short-term investments	129,933	91,059
Securities held to maturity	15,778	9,200
Securities available-for-sale	395,040	194,090
Restricted stock	14,447	10,092
Loans, net	1,953,968	1,069,366
Derivative assets	487	993
Total financial assets	2,509,653	1,374,800
Financial liabilities:
Deposits	2,286,212	1,054,327
Short-term borrowings	79,527	186,009
Long-term borrowings	60,000	60,000
Trust preferred debentures	3,863	0
Derivatives	71	325
Total financial liabilities	2,429,673	1,300,661
Total Fair Value
Financial assets:
Cash and short-term investments	129,933	91,059
Securities held to maturity	16,416	9,293
Securities available-for-sale	395,040	194,090
Restricted stock	14,447	10,092
Loans, net	1,992,323	1,080,820
Derivative assets	487	993
Total financial assets	2,548,646	1,386,347
Financial liabilities:
Deposits	2,252,241	1,040,402
Short-term borrowings	79,336	185,910
Long-term borrowings	59,491	59,954
Trust preferred debentures	3,689	0
Derivatives	71	325
Total financial liabilities	$ 2,394,828	$ 1,286,591