Fair Value - Summary of Carrying Value and Fair Value of Company's Financial Instruments (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities held to maturity (1)		$ 400,647	$ 416,863
Loans, net		3,869,007	3,790,255
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities held to maturity (1)	[1]	0	0
Time deposits with other banks		0	0
Loans, net		0	0
Deposit liabilities		0	0
Subordinated debt		0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities held to maturity (1)	[1]	391,867	414,472
Time deposits with other banks		0	0
Loans, net		0	0
Deposit liabilities		0	0
Subordinated debt		61,591	61,530
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities held to maturity (1)	[1]	0	0
Time deposits with other banks		12,475	12,493
Loans, net		3,852,712	3,760,754
Deposit liabilities		4,713,262	4,588,515
Subordinated debt		0	0
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities held to maturity (1)	[1]	400,647	416,863
Time deposits with other banks		12,553	12,553
Loans, net		3,861,868	3,786,063
Deposit liabilities		4,719,543	4,592,720
Subordinated debt		$ 70,591	$ 70,521

[1] See Note D for further detail of recurring fair value basis of individual investment categories.