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Share-Based Compensation Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options awarded		0
Unvested stock options forfeited	0	0
Accounting Standards Update 2016-09
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 0.3
Restricted Stock | Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted	38,778	22,503
Weighted average fair value per share	$ 40.57	$ 38.21
Shares vested	11,843
Restricted Stock | Key Employees | Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Jan. 01, 2019	Jan. 01, 2018
Percentage of shares vested on each anniversary of the grant date	16.50%	16.50%
Restricted Stock | Key Employees | Share-based Compensation Award, Tranche 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Jan. 01, 2020	Jan. 01, 2019
Percentage of shares vested on each anniversary of the grant date	16.50%	16.50%
Restricted Stock | Key Employees | Share-based Compensation Award, Tranche 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Jan. 01, 2021	Jan. 01, 2020
Percentage of shares vested on each anniversary of the grant date	17.00%	17.00%
Restricted Stock | Key Employees | Vesting Schedule Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Mar. 15, 2021	Mar. 15, 2020
Percentage of shares vested on each anniversary of the grant date	100.00%	100.00%
Percentage of stock award subject to vesting	50.00%	50.00%
Restricted Stock | Non Employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted	9,142	6,700
Weighted average fair value per share	$ 34.52	$ 38.49
Stock Options | Chief Executive Officer | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options awarded	0
Stock Options | Chief Executive Officer | Share-based Compensation Award, Tranche 2 | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options awarded			300,000
Stock Options | Chief Executive Officer | Vesting Schedule Two | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Dec. 31, 2019
Stock Options | Chief Executive Officer | Vesting Schedule One | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Dec. 31, 2018
Stock Options | Chief Executive Officer | Vesting Schedule Three | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Dec. 31, 2020
Time Based Option Award | Chief Executive Officer | Share-based Compensation Award, Tranche 3 | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted	300,000
Strike price per share	$ 50
Percentage of shares vested on each anniversary of the grant date	33.33%
Time Based Option Award | Chief Executive Officer | Vesting Schedule Two | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Dec. 31, 2019
Time Based Option Award | Chief Executive Officer | Vesting Schedule One | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Dec. 31, 2018
Time Based Option Award | Chief Executive Officer | Vesting Schedule Three | Employment Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting date	Dec. 31, 2020
Expiration date	Dec. 31, 2027

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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