Loans and Other Real Estate - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 35,031	$ 12,179
Current	4,889,640	4,448,268
Total Loans	4,924,671	4,460,447
Recorded Investment Greater than 89 Days and Still Accruing	78	0
Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21,917	4,353
Current	3,414,633	3,053,426
Total Loans	3,436,550	3,057,779
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,681	1,166
Current	387,549	335,569
Total Loans	389,230	336,735
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	951	1,047
Current	89,840	86,878
Total Loans	90,791	87,925
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,552	2,630
Current	331,738	327,224
Total Loans	335,290	329,854
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,423	0
Current	329,572	319,545
Total Loans	332,995	319,545
Recorded Investment Greater than 89 Days and Still Accruing	0	0
Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,507	2,983
Current	336,308	325,626
Total Loans	339,815	328,609
Recorded Investment Greater than 89 Days and Still Accruing	78	0
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	20,637	4,843
30-59 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14,944	1,477
30-59 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,084	173
30-59 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	358	533
30-59 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,406	743
30-59 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
30-59 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,845	1,917
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,855	1,222
60-89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,060	639
60-89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	220	243
60-89 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	210	13
60-89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	111
60-89 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
60-89 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	365	216
Greater Than 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,539	6,114
Greater Than 89 Days Past Due | Commercial, secured by real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,913	2,237
Greater Than 89 Days Past Due | Commercial, industrial and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	377	750
Greater Than 89 Days Past Due | Equipment finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	383	501
Greater Than 89 Days Past Due | Real estate - residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,146	1,776
Greater Than 89 Days Past Due | Real estate - construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,423	0
Greater Than 89 Days Past Due | Home equity and consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 1,297	$ 850