Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2009	Jun. 06, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized				1,500,000	815,000
Share-based compensation expense	$ 3,399,000	$ 3,854,000	$ 3,680,000
Tax benefit related to share-based compensation expense	1,300,000	1,500,000	1,400,000
Capitalized share-based compensation expense	0	0	0
Amount of reduction in net income due to share-based compensation expense	$ 2,100,000	$ 2,300,000	$ 2,200,000
Amount of reduction in diluted earning per share to share-based compensation expense	$ 0.08	$ 0.09	$ 0.09
Stock option plans remain outstanding	1,410,650	1,343,760	1,772,062	2,838,553
Weighted average grant date fair value	$ 6.60	$ 9.17	$ 9.87
Plan merged assets	$ 16,400,000
Dividends deducted	300,000
Tax benefit from dividends	$ 100,000
Shares outstanding, employee stock ownership plan	339,640
Percentage of total common shares outstanding	2.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized	843,024
Stock options granted	7,277,200
Stock options, exercise prices lower	$ 3.47
Stock options, exercise prices upper	$ 38.89
Purchase of shares	4,854,518
Stock option shares terminated	1,012,032
Stock option plans remain outstanding	1,410,650
Stock options outstanding, exercise prices lower	$ 15.62
Stock options outstanding, exercise prices upper	$ 38.89
Stock options vesting period	5 years
Options issued to non-employee advisors	0
Aggregate intrinsic value of options exercised and sold	$ 5,700,000	$ 8,400,000	$ 11,500,000
Total unrecognized compensation cost	$ 4,500,000
Expected recognition period of unrecognized compensation expense	2 years 8 months 12 days
Performance-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	5 years
Percentage of vesting annually at anniversary	20.00%
Number of RSU's expected to vest	66,651
Performance-based RSUs [Member] | Vesting after three years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of vesting RSUs	60.00%
Service-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of RSU's expected to vest	18,000
Number of forfeitures expected	0
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected recognition period of unrecognized compensation expense	2 years 4 months 24 days
Number of forfeitures expected	80,320	7,540	4,300
Stock-based compensation expense for restricted stock	$ 1,700,000	$ 2,300,000	$ 2,000,000
Total unrecognized compensation expense net of forfeitures	$ 1,100,000
Minimum [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	7 years
Minimum [Member] | Service-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	12 months
Maximum [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	10 years
Maximum [Member] | Service-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	14 months
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction in common stock available for grant	2
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock remained available for grants of awards						1,875,000
Minimum rate of exercise price granted	100.00%