Capital Structure - Additional Information (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) ClassOfCommonStock $ / shares shares	Jun. 30, 2017 USD ($) $ / shares shares	Feb. 28, 2017 USD ($)	Dec. 30, 2014 USD ($)
Equity, Class of Treasury Stock [Line Items]
Number of classes of common stock outstanding | ClassOfCommonStock			1
Acquisition of restricted stock from employees in connection with withholding tax payments (in shares) | shares	3,835	2,219	45,646	65,003
Withholding tax payments related to the vesting of restricted stock for total consideration	$ 226,000	$ 103,000	$ 2,790,000	$ 3,016,000
Weighted average purchase price prior to the vesting date (in dollars per share) | $ / shares	$ 58.82	$ 46.51	$ 61.12	$ 46.40
2014 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock authorized by board of directors up to						$ 20,000,000
2017 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Additional authorized amount					$ 100,000,000
Authorized increase in repurchase amount, 2018					40,000,000
Authorized increase in repurchase amount, 2019					40,000,000
Common stock purchased under the repurchase program (in shares) | shares	165,000		347,182
Common stock aggregate purchase price including commissions	$ 9,407,000		$ 20,346,000
Common stock average purchase price per share (in dollars per share) | $ / shares	$ 57.01		$ 58.60
2017 Repurchase Program | Minimum
Equity, Class of Treasury Stock [Line Items]
Authorized increase in repurchase amount					20,000,000
2017 Repurchase Program | Maximum
Equity, Class of Treasury Stock [Line Items]
Authorized increase in repurchase amount					$ 40,000,000
2014 and 2017 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock purchased under the repurchase program (in shares) | shares		230,022		423,984
Common stock aggregate purchase price including commissions		$ 11,316,000		$ 20,316,000
Common stock average purchase price per share (in dollars per share) | $ / shares		$ 49.20		$ 47.92