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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Income
Net income available to common stockholders	$ 39,634	$ 24,136	$ 76,313	$ 47,329
Diluted net income per share	$ 39,634	$ 24,136	$ 76,313	$ 47,329
Weighted-Average Shares
Net income available to common stockholders (in shares)	49,252,580	42,038,824	49,222,779	41,514,565
Effect of potentially dilutive stock options and restricted stock awards (in shares)	198,826	204,715	217,266	220,456
Diluted net income per share (in shares)	49,451,406	42,243,539	49,440,045	41,735,021
Per Share Amount
Net income available to common stockholders (in dollars per share)	$ 0.80	$ 0.57	$ 1.55	$ 1.14
Diluted net income per share (in dollars per share)	$ 0.80	$ 0.57	$ 1.54	$ 1.13