Fair Value Measurements - Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale securities	$ 2,077,616	$ 1,630,567
Derivative assets	101,027	53,202
Derivative liabilities	93,514	51,605
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	30,004	29,796
U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	384,637	367,994
Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	554,723	495,830
Assets measured at fair value, Available for sale securities	554,723
Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	935	1,190
Assets measured at fair value, Available for sale securities	935
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	2,816	4,287
Assets measured at fair value, Available for sale securities	2,816
States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	37,138	11,057
Other Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	9,345	14,286
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale securities	259	225
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale securities	2,075,989	1,628,719
Derivative assets	101,027	53,202
Derivative liabilities	93,514	51,605
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale securities	1,368	1,623
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	2,076,249	1,629,271
Assets measured at fair value, Available for sale equity securities	1,367	1,296
Assets measured at fair value, Available for sale securities	2,077,616	1,630,567
Derivative assets	101,027	53,202
Assets measured at fair value, Total	2,178,643	1,683,769
Liabilities measured at fair value, Total	93,514	51,605
Fair Value, Measurements, Recurring [Member] | U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	30,004	29,796
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	384,637	367,994
Fair Value, Measurements, Recurring [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	554,723	495,830
Fair Value, Measurements, Recurring [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	935	1,190
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	2,816	4,287
Fair Value, Measurements, Recurring [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	37,138	11,057
Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	9,345	14,286
Fair Value, Measurements, Recurring [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	91,032	50,017
Fair Value, Measurements, Recurring [Member] | Not for Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	9,995	3,185
Fair Value, Measurements, Recurring [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	1,229	1,168
Fair Value, Measurements, Recurring [Member] | Insurance Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	138	128
Fair Value, Measurements, Recurring [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	1,056,651	704,831
Fair Value, Measurements, Recurring [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	91,992	50,510
Fair Value, Measurements, Recurring [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	1,522	1,095
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	259	225
Assets measured at fair value, Available for sale securities	259	225
Assets measured at fair value, Total	259	225
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	121	97
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Insurance Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	138	128
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	2,075,317	1,628,087
Assets measured at fair value, Available for sale equity securities	672	632
Assets measured at fair value, Available for sale securities	2,075,989	1,628,719
Derivative assets	101,027	53,202
Assets measured at fair value, Total	2,177,016	1,681,921
Liabilities measured at fair value, Total	93,514	51,605
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	30,004	29,796
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	384,637	367,994
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	554,723	495,830
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	3	6
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	2,816	4,287
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	37,138	11,057
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	9,345	14,286
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	91,032	50,017
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Not for Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	9,995	3,185
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	672	632
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	1,056,651	704,831
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	91,992	50,510
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	1,522	1,095
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	932	1,184
Assets measured at fair value, Available for sale equity securities	436	439
Assets measured at fair value, Available for sale securities	1,368	1,623
Assets measured at fair value, Total	1,368	1,623
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	932	1,184
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	$ 436	$ 439