Stockholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2012	Oct. 31, 2016	Jul. 31, 2015	Feb. 28, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized	500,000				500,000								500,000	500,000
Preferred stock, par value	$ 0.01				$ 0.01								$ 0.01	$ 0.01
Authorized to purchase of common stock under the stock repurchase program	$ 485,000,000												$ 485,000,000				$ 25,000,000	$ 25,000,000	$ 25,000,000
Cumulative repurchase of common stock	16,100,000												16,100,000
Aggregate cost of repurchase of common stock													$ 464,900,000
Dividend declared and paid per share	$ 0.19	$ 0.19	$ 0.19	$ 0.19	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.17	$ 0.17	$ 0.17	$ 0.17
Dividend declared per share													$ 0.76	$ 0.72	$ 0.68
Aggregate dividend declared for the year													$ 13,600,000	$ 13,000,000	$ 12,200,000
Option Outstanding and vested	937,000				1,540,000								937,000	1,540,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future awards granted or issued under plans	100,000												100,000
Shares authorized	700,000												700,000
Hours of work per week													20 hours
Duration of purchase periods under employee stock purchase plan													6 months
Holding period of stocks acquired under employee stock purchase plan													1 year
Value used to derive maximum number of shares per participant for employee stock purchase													$ 12,500
Employee maximum elected percentage reduction of compensation to purchase shares	10.00%												10.00%
Exercise price rate of fair value													85.00%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value for RSUs granted													$ 39.73	$ 37.87	$ 31.50
Number of shares received per restricted stock unit on lapse of restrictions and vesting condition met													1
Value of RSUs vested and converted to common stock													$ 8,700,000	$ 6,600,000	$ 4,600,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised													$ 4,500,000	$ 3,700,000	$ 400,000
1996 Equity Plan [Member] | Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future awards granted or issued under plans	0												0
2006 Director Plan [Member] | Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future awards granted or issued under plans	0												0
Shares authorized	450,000,000												450,000,000
Shares returned																80,000
Option Outstanding and vested	100,000												100,000
1996 Director [Member] | Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future awards granted or issued under plans	0												0
Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan extended term													10 years
Equity incentive plan expiration													2026-05
Increase in number of shares issuable under plan													2,000,000
Equity Incentive Plan [Member] | Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future awards granted or issued under plans	2,600,000												2,600,000
Shares authorized																6,350,000
Shares returned																713,275
Option expiration period													10 years
Equity Incentive Plan [Member] | Equity Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vested period													4 years
Equity Incentive Plan [Member] | Equity Plan [Member] | Non-Employee Directors [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vested period													1 year