Stockholders' Equity - Dividend Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2011	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 06, 2018	Jun. 07, 2018	Apr. 05, 2018	Dec. 07, 2017	Sep. 07, 2017	Jun. 08, 2017	Apr. 06, 2017
Dividends Payable [Line Items]
Per Share Amount		$ 0.070	$ 0.055	$ 0.210	$ 0.165
Installment FY 2018 [Member]
Dividends Payable [Line Items]
Record Date				Mar. 22, 2018
Payment Date				Apr. 05, 2018
Per Share Amount	$ 0.070
Dividend Payment								$ 1,351
Installment 1 FY 2018 [Member]
Dividends Payable [Line Items]
Record Date				May 22, 2018
Payment Date				Jun. 07, 2018
Per Share Amount	0.070
Dividend Payment							$ 1,353
Installment 3 FY 2018 [Member]
Dividends Payable [Line Items]
Record Date				Aug. 22, 2018
Payment Date				Sep. 06, 2018
Per Share Amount	0.070
Dividend Payment						$ 1,369
Installment 1 FY 2017 [Member]
Dividends Payable [Line Items]
Record Date				Mar. 22, 2017
Payment Date				Apr. 06, 2017
Per Share Amount	0.055
Dividend Payment												$ 1,029
Installment 2 FY 2017 [Member]
Dividends Payable [Line Items]
Record Date				May 24, 2017
Payment Date				Jun. 08, 2017
Per Share Amount	0.055
Dividend Payment											$ 1,036
Installment 3 FY 2017 [Member]
Dividends Payable [Line Items]
Record Date				Aug. 23, 2017
Payment Date				Sep. 07, 2017
Per Share Amount	0.055
Dividend Payment										$ 1,055
Installment 4 FY 2017 [Member]
Dividends Payable [Line Items]
Record Date				Nov. 22, 2017
Payment Date				Dec. 07, 2017
Per Share Amount	$ 0.055
Dividend Payment									$ 1,060