Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 08, 2016	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 3,091,000	$ 3,399,000	$ 3,854,000
Tax benefit related to share-based compensation expense	1,200,000	1,300,000	1,500,000
Capitalized share-based compensation expense	0	0	0
Amount of reduction in net income due to share-based compensation expense	$ 1,900,000	$ 2,100,000	$ 2,300,000
Amount of reduction in diluted earning per share to share-based compensation expense	$ 0.08	$ 0.08	$ 0.09
Stock option plans remain outstanding	1,584,435	1,410,650	1,343,760		1,772,062
Weighted average grant date fair value	$ 4.14	$ 6.60	$ 9.17
Dividends deducted	$ 400,000
Tax benefit from dividends	$ 100,000
Shares outstanding, employee stock ownership plan	335,334
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	2,251,074
Stock options granted	8,159,000
Stock options, exercise prices lower	$ 3.47
Stock options, exercise prices upper	$ 39.19
Purchase of shares	5,222,603
Stock option shares terminated	1,351,962
Stock option plans remain outstanding	1,584,435
Stock options outstanding, exercise prices lower	$ 23.84
Stock options outstanding, exercise prices upper	$ 39.19
Stock options vesting period	5 years
Options Outstanding, Weighted-Average Remaining Contractual Life (Years)	7 years
Options issued to non-employee advisors	0
Aggregate intrinsic value of options exercised and sold	$ 4,200,000	$ 5,700,000	$ 8,400,000
Total unrecognized compensation cost	$ 5,700,000
Expected recognition period of unrecognized compensation expense	3 years 1 month 6 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	30,380
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	23,400
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 3 months 18 days
Number of forfeitures expected	68,300	80,320	7,540
Stock-based compensation expense for restricted stock	$ 1,000,000	$ 1,700,000	$ 2,300,000
Total unrecognized compensation expense net of forfeitures	$ 600,000
Maximum [Member] | Service-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	14 months
Minimum [Member] | Service-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	12 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] | 2016 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock remained available for grants of awards				2,000,000
Common Stock [Member] | 2016 Stock Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of award (in years)	7 years
Common Stock [Member] | 2016 Stock Incentive Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Rate of exercise price for equity award granted	100.00%