Employee Benefits and Incentive Plans - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2013	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued			17,168
Fair value of common stock issued			$ 500,000
Stock based payment award vesting period			3 years 8 months 12 days
Fair value of restricted stock			$ 12,200,000
Common stock, shares authorized			475,000	475,000
Common stock, shares issued			85,459	84,272
Compensation expense			$ 22,900,000	$ 15,600,000	$ 10,400,000
Shares issued from the Employee Stock Purchase Plan			286,141	271,255
Net income effect of share-based compensation expense			$ 14,700,000	$ 10,100,000	$ 6,500,000
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based payment award vesting period			4 years
Vesting Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award exercisable rate		25.00%
2006 EIP and 2013 LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued			645,568
Unrecorded and unrecognized compensation expense related to unvested share based compensation stock options			$ 2,700,000	9,300,000
Unrecorded and unrecognized compensation expense related to unvested share based compensation on restricted stock, Recognition period			9 months 18 days
2013 LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecorded and unrecognized compensation expense related to unvested share based compensation on restricted stock, Recognition period			3 years 9 months
Unrecorded and unrecognized compensation expense related to unvested share based compensation on restricted stock			$ 42,100,000	45,100,000
Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based payment award vesting period			1 year
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued		470,900
Restricted Stock [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based payment award vesting period			3 years
Restricted Stock [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based payment award vesting period			4 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued		470,900
Performance-Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based payment award vesting period			2 years 8 months 12 days
Shares issued		157,500
Fair value of performance stock			$ 4,300,000
Performance-Based Restricted Stock Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contingent right to receive common stock shares		0
Performance-Based Restricted Stock Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contingent right to receive common stock shares		1.75
Stock Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized	1,000,000				1,000,000
Percentage of annual compensation designated by employees	50.00%				50.00%
Maximum shares purchasable per person	2,000
Percentage of shares purchase price to market closing price	85.00%
Maximum voting power	5.00%
Maximum stock purchased to fair market value	$ 25,000
Common stock, shares issued			557,396
Compensation expense			$ 1,200,000	$ 1,100,000	$ 300,000
Shares issued from the Employee Stock Purchase Plan			286,141