Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 4,220,000	$ 3,050,000
Number of shares available to non-employee directors through the non qualified stock option plan for non-employee directors, other than annual meeting			2,000
Share-based compensation arrangement by share-based payment award options exercisable intrinsic value per share			$ 0
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised during the period	$ 1,400,000	$ 200,000	$ 2,800,000	4,100,000
Stock-based compensation expense for stock options included in non-interest expense	600,000	800,000	1,200,000	$ 1,200,000
Total unrecognized compensation expenses	3,700,000		$ 3,700,000
Unrecognized compensation cost, weighted-average period, years			2 years
Stock options, granted			2,000	52,000
Restricted Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award issued with a vesting period, years			3 years
Stock-based compensation expense for stock options included in non-interest expense	1,400,000	$ 900,000	$ 2,700,000	$ 1,800,000
Total unrecognized compensation expenses	9,500,000		$ 9,500,000
Unrecognized compensation cost, weighted-average period, years			2 years 2 months 12 days
Nonqualified Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award issued with a vesting period, years			3 years
Employee options expire after issuance, years			7 years
Nonqualified Stock Option Plan [Member] | Non Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available to non-employee directors through the non qualified stock option plan for non-employee directors, other than annual meeting			0
Non-Employee Directors Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of non-employee directors stock awards on the date of grant	$ 25,000
Number of common stock shares issued	7,657
Stock-based compensation expense	$ 300,000
Non-Employee Directors Stock Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares issued as awards	50,000		50,000