Fair Value Accounting - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended	12 Months Ended
		Jun. 30, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired Financing Receivable, Recorded Investment		$ 105,634	$ 105,634		$ 99,209
Aggregate carrying amount of impaired loans	[1]	8,295	8,295		10,909
Impaired loans with an allowance recorded		(3,878)	(3,878)		(4,239)
Other assets acquired through foreclosure		31,000	31,000		47,800
Goodwill		$ 289,895	$ 289,895		$ 289,967
Common Stock, Shares, Issued		106,931,341	106,931,341		106,371,093
Collateralized debt obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities contained credit losses			0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans with an allowance recorded		$ (3,900)	$ (3,900)		$ (4,200)
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt, Input Value				5.21%	5.66%
Period of basis point spread		3.91%			4.66%
Percentage of LIBOR		1.29917%			1.00%
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate carrying amount of impaired loans		$ 4,417	4,417		$ 6,670
Other assets acquired through foreclosure		30,988	30,988		47,815
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired Financing Receivable, Recorded Investment		80,992	80,992		67,408
Aggregate carrying amount of impaired loans		4,417	4,417		6,670
Other assets acquired through foreclosure		$ 30,988	$ 30,988		$ 47,815

[1] Includes TDR loans of $6.9 million and $2.5 million at June 30, 2017 and December 31, 2016, respectively.