Net Income Per Share - Reconciliation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Income
Net income available to common stockholders	$ 41,056	$ 39,634	$ 79,873	$ 76,313
Diluted net income per share	$ 41,056	$ 39,634	$ 79,873	$ 76,313
Weighted-Average Shares
Net income available to common stockholders (in shares)	49,432,167	49,252,580	49,400,770	49,222,779
Effect of potentially dilutive stock options and restricted stock awards (in shares)	117,720	198,826	144,382	217,266
Diluted net income per share (in shares)	49,549,887	49,451,406	49,545,152	49,440,045
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.83	$ 0.80	$ 1.62	$ 1.55
Diluted net income per share (in dollars per share)	$ 0.83	$ 0.80	$ 1.61	$ 1.54