Investment Securities - Summary of Securities Available for Sale in an Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	$ 165,904	$ 564,710
Less than 12 months, Unrealized Losses	2,399	10,569
12 months or longer, Fair Value	272,439	274,399
12 months or longer, Unrealized Losses	18,779	7,971
Total, Fair Value	438,343	839,109
Total, Unrealized Losses	21,178	18,540
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	348	1,415
Less than 12 months, Unrealized Losses	3	6
12 months or longer, Fair Value	0	0
12 months or longer, Unrealized Losses	0	0
Total, Fair Value	348	1,415
Total, Unrealized Losses	3	6
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	17,795	144,307
Less than 12 months, Unrealized Losses	235	3,291
12 months or longer, Fair Value	226	885
12 months or longer, Unrealized Losses	1	5
Total, Fair Value	18,021	145,192
Total, Unrealized Losses	236	3,296
Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	26,496	108,072
Less than 12 months, Unrealized Losses	51	502
12 months or longer, Fair Value	0	71,736
12 months or longer, Unrealized Losses	0	744
Total, Fair Value	26,496	179,808
Total, Unrealized Losses	51	1,246
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	0	0
12 months or longer, Unrealized Losses	0	0
Total, Fair Value	0	0
Total, Unrealized Losses	0	0
Commercial Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	14,025	173,039
Less than 12 months, Unrealized Losses	99	2,676
12 months or longer, Fair Value	0	45,251
12 months or longer, Unrealized Losses	0	131
Total, Fair Value	14,025	218,290
Total, Unrealized Losses	99	2,807
Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	11,202	135,174
Less than 12 months, Unrealized Losses	675	3,252
12 months or longer, Fair Value	254,882	140,965
12 months or longer, Unrealized Losses	14,897	4,999
Total, Fair Value	266,084	276,139
Total, Unrealized Losses	15,572	8,251
Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	2,703
Less than 12 months, Unrealized Losses	0	842
12 months or longer, Fair Value	4,347	2,000
12 months or longer, Unrealized Losses	1,702	500
Total, Fair Value	4,347	4,703
Total, Unrealized Losses	1,702	1,342
Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	12,984	13,562
12 months or longer, Unrealized Losses	2,179	1,592
Total, Fair Value	12,984	13,562
Total, Unrealized Losses	2,179	1,592
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	96,038	0
Less than 12 months, Unrealized Losses	1,336	0
12 months or longer, Fair Value	0	0
12 months or longer, Unrealized Losses	0	0
Total, Fair Value	96,038	0
Total, Unrealized Losses	$ 1,336	$ 0